REPORT NO. FRA/ORD-

REAR-END TRAIN MARKER LIGHT EVALUATION

Denwood Ross I11 Daniel Grieser

(Laboratory Tests)

Del i a Treaster, M.S. Louis Ti jer ina, Ph.D.

(Human Factors Tests)

BATTELLE 505 King Avenue

Columbus, Ohio 43201

September 7, 1990

FINAL REPORT

TECHNICAL TASK NO. 7 CONTRACT NO. DTFR53-86-C-00006

Document i s Available t o the U.S. Public Through the National Technical Information

Service, Springfield, V i rg in ia 22161

Prepared f o r

U . S . DEPARTMENT OF TRANS PORTATION FEDERAL RAILROAD ADMINISTRATION

Washington, D.C. 20590

NOTICE

The United S t a t e s Government does n o t endorse produc ts o r manufacturers. Trade o r manufacturers ' names appear h e r e i n s o l e l y because they are con- s i d e r e d e s s e n t i a l t o the o b j e c t o f this r e p o r t .

NOTICE

Thi s document i s disseminated under t h e sponsorship of t h e Department of T ranspor t a t i on i n t h e i n t e r e s t o f in format ion exchange. The United S t a t e s Govern- ment assumes no l i a b i l i t y f o r i t s c o n t e n t s o r use t h e r e o f .

This report is a work prepared for the United States by Battelle. In no event shall either the United States or Battelle have any responsibility or liability for the con- sequences of any use, misuse, inability to use, or reli- ance upon the information contained herein, nor does either warrant or otherwise represent in any way the accuracy, adequacy, efficacy, or applicability of the contents hereof.

Technical Report Documentotion Pog.

I. Report No. 2 . Cover~rment Access~on No. 3. R e c ~ p ~ e n t ' r Catalog No.

I I I

4. Titlm ond Subtttle ( 5. Report Dot. I September 7, 1990 REAR-END TRAIN MARKER LIGHT EVALUATION -

6. Perform~ng Organixotion Code

8. Performinp Organ~xotion Report No.

Denwood Ross 111, Daniel Gr ieser (Lab Tests), D e l i a Treaster, Louis T i j e r i n a ( F i e l d Tests)

9. Performing Orgaixot ion Namo ond Address 10. Work U n ~ t No. (TRAIS)

BATTELLE 505 King Avenue 1 1 . Contract or Grant NO.

Columbus, Ohio 43201 DTFR53-86-C-00006, Task 7 13. Typo o f Report ond Period Covered

12. Sponsoring Agoncy Nome ond Addross F ina l Report Federal Ra i l road Admin is t ra t ion January 1988-September 1990 O f f i c e of Research & Development 1 400 Seventh St ree t , S.W. I

14. Agency Code

Washinqton. ., D.C. 20590 I tTE Sponsoring

I S . Supplementory Notes

A l l rear-end t r a i n marker l i g h t s u n t i l r e c e n t l y were incandescent bulbs o f almost i d e n t i c a l design. With t h e advent o f cabooseless t r a i n s and battery-powered end- o f - t r a i n devices, new technologies us ing low-power LED and xenon f lash tube l i g h t s were developed. Because o f unce r ta in t i es i n o f f - a x i s l i g h t i n t e n s i t y d i s t r i b u t i o n , t h e FRA s~onsored t h i s research study t o evaluate d i f f e r e n t types o f markers i n t he contex t of cu r ren t Federal regual t i o n s (CFR Pa r t 221 ).

Laboratory t e s t s were conducted on the t r a i n rear-end marker devices from four manu- fac tu re rs . These inc luded incandescent bulbs, LED arrays, and two d i f f e ren t xenon f l a s h tube devices. Both r e d and amber lenses were tes ted on two o f t h e devices. Chromat ic i ty ( c o l o r ) measurements were made over a .range of 380 t o 780 m i l 1 imicrons wavelength. Peak i n t e n s i t y measurements were then made us ing a telephotometer a t d is tances o f 25 and 100 feet, both a t the geometric center and up t o t 9 0 degrees v e r t i c a l l y and h o r i z o n t a l l y from center. E f fec t i ve i n t e n s i t y values were ca lcu la ted based on t ime i n t e g r a t i a n o f t he pulse shape, us ing standard IES formulae.

A f i e l d t e s t was then conducted t o assess the r i s i s b i l i t y t o human observers o f t h e t e s t markers d i f f e r i n g i n lamp type, co lo r , cyc le (pulsed o r steady) and i n t e n s i t y . Both sub jec t i ve assessments and v i s u a l de tec t i an data wwe co l lec ted , us ing a popu- l a t i o n o f 24 volunteers. Tests were s e t up on a 1000-f t s t r e t c h o f dark voad a t B a t t e l l e ' s West Je f fe rson f a c i l i t y * Po in t o f angular d e t e c t i ~ n was measured by s low ly r o t a t i n g each device. On-axis assessment was done by an "A-0" comparison of d i f f e r e n t marker combinations. F i e l d t e s t data d i d d i s t i n g u i s h among markers.

17. Key Words 18. Dtstr~button Stotommt -

T r a i n rear-end markers, l i g h t i-ntensi-ty Document a v a i l a b l e through the d i s t r i bu t i . on , m a ~ k e r c o l o r d i s t r t b u t i o r Nat ional Technical 1nformati.on Service human f a c t ~ r s t e s t s 5285 P w t Royal aoad

Spr i ng f i'el d B YA 221 61

I

19. Security Clossil. (of this rmport) 20. Socurity Classif. (of this page) 21. No. o f Popes 22. Price

Unc lass i f ied Uncl ass i f i.ed 106

form DOT F 1700.7 (8-72) Reproduction of completed page outhorixed

TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY .................................................. v

1.0 INTRODUCTION .................................................. 1

2.0 TEST OBJECTIVE ................................................ 3

3.0 LABORATORY MEASUREMENTS ....................................... 3

4.0 LABORATORY RESULTS ............................................ 11

4.1 Test Data ................................................ 11 4.2 Observat ions ............................................. 16 4.3 Comparison w i t h ETL Test Resu l ts ......................... 22

5.0 FIELD EXPERIMENTS ............................................ 27

5.1 Experimental Backgroud ............................... 28 5.2 Human Subjects f o r Experiments ........................... 30 5.3 Experimental Apparatus ................................... 31 5.4 Experimental Procedure ............................... 36

6.0 FIELD EXPERIMENTAL RESULTS AND DISCUSSION ..................... 41

6.1 V i s i b i l i t y Rat ings ....................................... 41 6.2 P a i r Comparisons f o r V i s i b i l i t y .......................... . 43 6.3 Detec t ion Angles f rom .................................... Simulated Approach Along 11° Track 47 6.4 Discuss ion o f Resu l ts 55

7.0 SUMMARY AND CONCLUSIONS ....................................... 61

7.1 Laboratory Tests ......................................... 61 7.2 F i e l d Tests .............................................. 62 7.3 Recommendations f o r Fu tu re Research ...................... 64

REFERENCES ......................................................... 65

APPENDIX B . ANGULAR INTENSITY DATA AT 25 FEET ..................... B-1

APPENDIX C . ANGULAR :INTENSITY DATA AT 100 FEET .................... C - 1

APPENDIX D . MATHEMATICAL DESCRIPTIONS USED I N THE DEVELOPMENT OF THE CURVED APPROACH SIMULATION ........................ D - 1

APPENDIX E . STATISTICAL TESTS FOR MARKERS ......................... E-1

LIST OF FIGURES

Page

Figure 3.1 . Photograph o f Test Setup .............................. 5

Figure 3.2 . Dynamic Sciences L imi ted .............................. 8

Figure 3.3 . Pulse E lec t ron ics . I n c ................................ 8

Figure 3.4 . Star Headl ight and Latern Company ..................... 9

Figure 3.5 . Trans i t Control Systems ............................... 9

Figure 4.1 . DSL Lamp #2957 a t 0 Degrees ........................... 13

Figure 4.2 . Pulse Lamp #205 a t 0 Degrees .......................... 13

Figure 4.3 . Sta r Lamp Y2 a t 0 Degrees ............................. 14

Figure 4.4 . TCS Lamp # I02 a t 0 Degrees ............................ 14

Figure 4.5 . Idea l i zed I n t e n s i t y P r o f i l e o f Pulse Lamp #203 View Showing Ext ra Measurements ............ From

Observer's 17

Figure 5.1 . Geometry o f a Curved-Track Approach Toward a Rear-End Marker Device .................................. 29

Figure 5.2 . Schematic Diagram o f Equipment f o r F i e l d Tests ........ 33

Figure 5.3 . Arrangement o f Equipment a t Marker S i t e ............... 33

Figure 5.4 . Photographs o f Equipment Set Up a t Marker S i t e ........ 34

Figure 5.5 . Pos i t i on o f Subjects During Test ing ................... 35

Figure 5.6 . ExperTmental Test S i te . Looking From Observer ............. S i t e Toward Rear-End Marker S i te . 1000-f t Away 35

Figure 5.7 . Marker S t a r t i n g Pos i t ion . Re la t i ve t o Subject ......... 38

Figure 5.8 . Figure 6.1 . Empir ica l Propor t ions o f Ratings f o r V i s i b i 1 i t y "Good"

o r "Very Goodu. and 95 Percent Confidence I n t e r v a l .... 44

Figure 6.2 . Thi rs tone Class V I n t e r v a l Scale o f Rear-End T ra in Marker V i s i b i l i t y . 1000' Tangent Track Condi t ion ...... 49

Figure 6.3 . Side Views o f Rear-End Markers Used i n Tests .......... 52

LIST OF TABLES

Page

Table 3-1. Equipment Used i n Laboratory Experiments .............. 4

Table 3-2. Desc r i p t i on o f Rear-End Marker Devices ................ 6

Table 4-1. Summary o f 1931 and 1976 CIE Ch roma t i c i t y Coordinates. 12

Table 4-2. Summary o f Lamp Duty Cycles ........................... 15

Table 4-3. I n t e n s i t y Values f o r DSL Rear-End Markers ............. 18

Table 4-4. I n t e n s i t y Values f o r Pulse Rear-End Markers ........... 19

Table 4-5. I n t e n s i t y Values f o r S t a r Rear-End Markers ............ 20

Table 4-6. I n t e n s i t y Values f o r TCS Rear-End Markers. ............ 2 1

Table 4-7. Comparison of Rear-End Marker L i g h t I n t e n s i t y Tests.. . 24

Table 4-8. Comparison o f L i g h t I n t e n s i t y Measurements Under S i m i l a r Test Condi t ions ............................... 26

Table 5-1. D i s t r i b u t i o n o f Subjects i n t h e FRA Marker F i e l d Test by Age and Gender ...................

Rear-End T r a i n 31

Table 5-2. D e s c r i p t i o n o f Rear-End Marker Types and Cond i t ions ... 3 1

Table 6-1. Subject Rat ings o f Rear-End T r a i n Marker V i s i b i l i t y A t O 0 1000 Foot Approach (N = 24). . ... . . . . . . . . . ... .. .. 4 2

Table 6-2. P ropo r t i on Ma t r i x , P, Showing t h e P ropo r t i on o f Subjects Who Judged t h e Marker a t t h e V i s i b l e Than The Marker a t t h e Side ..............,....

Top t o be More 46

Table 6-3. The Standard Normal Deviate M a t r i z , Z, Showing t h e P ropo r t i on o f Subjects Who Judged t h e Marker a t t h e Top t o be More V i s i b l e Than t h e Marker a t t h e Side .... 48

Table 6-4. Mean Per Marker, Across Subjects , o f Median De tec t i on Angles, I n Degrees .................................... 5 1

Table 6-5. Contingency Table o f Mean Detec t ion Angles, Co lo r (Red, Yel low) ByManu fac tu re r ( P u l s e d S t a r , TCS) ...... 54

Table 6-6. Contingency Table o f Mean Detec t ion Angles, Co lo r (Red, Yel low) By Cyc le (Pulsed, Steady), S t a r Markers. 54

PREFACE

B a t t e l l e wishes t o acknowledge and thank the f o u r manufacturers who

cont r ibu ted rear-end marker devices f o r use i n t h i s study: Dynamic Sciences

Limited; Pulse E lec t ron ics , Inc.; S ta r Head1 i g h t and Lantern Company; and

T rans i t Contro l Syste~lis.

The authors wish t o acknowledge the many people who con t r i bu ted t o

t h i s e f f o r t . Thanks t o Mr . Garold Thomas, FRA's COTR, and Mr . Howard Moody

( fo rmer ly o f t he FRA) f o r t h e i r techn ica l assistance and con t r i bu t i ons .

Thanks a l so t o Mr . Ernest ('Corky") Dykeman o f ETL Laborator ies f o r he lp ing t o

" s o r t t h ings out".

M r . Steven Kiger, R&R Research o f Columbus, Ohio, served as a

consu l tan t t o B a t t e l l e on r a i l r oad operat ions. His comments and recommend-

a t i ons were h e l p f u l . D r . Stan Smith, p ro fessor emeritus o f t h e Ohio S ta te

Un ive rs i t y , served as a consu l tan t on v i s ion : h i s recommendations and advise

were q u i t e b e n e f i c i a l . Ms. Cheryl Jackson and Mr . Malcolm "Skip" Warren, both

from t h e Ohio S ta te Un ive rs i t y , served as student i n t e r n s du r ing the f i e l d

t e s t and con t r i bu ted t o the prepara t ion o f t h i s repor t . The d i l i g e n c e and

i n t e l l i g e n c e w i t h which they c a r r i e d ou t t h e i r du t i es made t h i s p r o j e c t run

much more smoothly than i t might have otherwise.

Messrs. Donald Ahlbeck, Denwood Ross, Jim Dye, and Doug Erwin, a l l

o f B a t t e l l e , prov ided admin i s t ra t i ve and techn ica l support f o r which s incere

thanks are extended. D r . G i ra rd Levy, B a t t e l l e , con t r i bu ted s u b s t a n t i a l l y t o

development o f t he methodology used i n t h i s study and prov ided.usefu1

e d i t o r i a l comments on t h i s f i n a l r e p o r t f o r which we a re g r a t e f u l . F i n a l l y ,

t he authors wish t o extend thanks t o a l l t he people who p a r t i c i p a t e d i n t he

l a t e - n i g h t t e s t sessions.

EXECUTIVE S W R Y

Laboratory Tests

Laboratory tests were conducted on the train rear-end marker devices

from four manufacturers. Chromaticity (color) measurements were made for each

device to determine irradiance versus wavelength over a range from 380 to 780 millimicrons. Peak intensity measurements were made using a telephotometer at

distances of 25 and 100 ft, both on the geometric center and up to &90° from

this center on the horizontal and vertical axes. For the pulsed lamps, effec-

tive intensities were calculated from peak intensities and integrating the

pulse shape versus time, and using the appropriate formula from the - IES

Lightinq Handbook.

Results from these tests showed that all units met the FRA color

range requirements. For the slower pulsed units (Pulse, Star -- typically a 114 second pulse duration), peak intensities on-axis exceeded the FRA minimum

of 100 candela. Off-axis (k15O horizontally, *5O vertically) , the Pulse devices fell near or below the FRA minimum of 50 candela; while the Star

devices (particularly with the amber lens) exceeded the minimum. Effective

intensity for these units (in candela-seconds), based on the IES formula, fell

below the given minima, except for the Star units with amber lenses.

For the xenon flash tube devices (DSL, TCS -- typically a 20 micro- second pulse duration), peak intensities exceeded the FRA maximum of 1000

candela. Effective intensities for the DSL units exceeded the FRA minimum of

100 on axis, but fell below the FRA minimum of 50 off axis. Effective inten-

sities for the TCS units fell below 1.0, a factor greater than 100 below the

FRA minimum. Comparison of these results with the results from tests conducted by

EPL Testing Laboratories, Inc., on the same or similar devices showed that

Battelle's peak intensity measurements were substantially lower than ETL's.

Direct comparison of measurements with both sets of equipment on three of the

devices, using the same set-up procedures, showed good correlation between

results. Based on this comparison, we conclude that the major differences in

i n t e n s i t y values are t h e r e s u l t o f device mounting procedures. Where B a t t e l l e

chose the geometric center o f t he device f o r i t s measurements, ETL chose the

lamp "hot spot" (po in t o f maximum i n t e n - s i t y ) f o r i t s readings. I n f u t u r e

t e s t i n g , t h e device mounting pro toco l must be taken i n t o cons idera t ion so t h a t

consistency i n r e s u l t s may be achieved.

F ie l d ( H m n Factors) Tests

A f i e l d t e s t was conducted t o assess the v i s i b i l i t y t o human obser-

vers o f a sample o f rear-end t r a i n markers d i f f e r i n g i n lamp type, c o l o r ,

cyc le (pul sed o r steady) and i n t e n s i t y . Both sub jec t i ve assessments and

v i sua l de tec t i on da ta were co l lec ted . The f o l l o w i n g i s a summary o f r e s u l t s

and conclusions w i t h respect t o v i s i b i l i t y o f t h e markers tested:

1. A l l markers used i n t h i s f i e l d t e s t a f fo rded adequate o f f - a x i s

de tec t ion , under t h e cond i t ions o f t h e t e s t , us ing t h e 1000 f t

t r a c k stopping d is tance c r i t e r i o n ;

2. A l l markers used i n t h i s f i e l d t e s t were v i s i b l e t o a l l sub-

j e c t s i n a 1000 f t on-axis viewing c o n d i t i o n which s i m u l a t e d

an approach on tangent t rack;

3. F i e l d t e s t data d i d d i s t i n g u i s h among markers, desp i te t h e

equal i t y o f markers w i t h reference t o an acceptabl elunaccep-

t a b l e th resho ld f o r a f f o r d i n g a t l e a s t 1000 f t o f t r a c k

stopping d is tance upon de tec t i on du r ing a 15-mph slow approach.

4. Markers were ranked i n order o f o f f - a x i s d e t e c t i b i l i t y . The

S ta r u n i t s had detec t ion angles from 155" t o 164'. A l l o the r

u n i t s had detec t ion angles from 84" t o 91". A l l were de tec t -

ab le w i t h i n t h e desi red minimum viewing angle o f 57".

5. Using the o f f - a x i s de tec t ion t e s t cond i t ions , S ta r . markers were

f a r more r e a d i l y detected than any o f t h e o ther makes. When

corrected f o r t h e f a c t t h a t 90° i s t h e l a rges t viewing angle o f

p r a c t i c a l i n t e r e s t , t h e Star markers are s t i l l t h e best, bu t

t h e i r s u p e r i o r i t y i s reduced subs tan t ia l l y .

6. Color e f f e c t s on o f f - a x i s de tec t ion were no t simple. Given

b l i n k i n g markers such as t h e TCS Xenon devices, ye l l ow seems t o

o f f e r an advantage over red. For markers such as t h e b l i n k i n g

S ta r devices, red seems t o o f f e r an advantage over ye1 low.

7. S i m i l a r l y , c o l o r and cyc le (pulsed o r steady) do no t have

simple e f f e c t s w i t h markers such as the Star lamps. Under t h e

o f f - a x i s de tec t ion cond i t ions o f t he t e s t , b l i n k i n g red markers

were detected e a r l i e r than steady red markers. However, steady

ye l l ow markers were detected more r e a d i l y than b l i n k i n g ye l l ow

markers.

8. Subject ive evaluat ions o f v i s i b i 1 i t y ( ra t i ngs , rankings, and

sca l i ng of t he markers) d i f f e r e n t i a t e d among the markers: S tar

and DSL markers were judged most v i s i b l e o f t h e l o t tested.

9. The marker ind ica ted by t h e f i e l d t e s t data as being most

read i l y d e t e c t i b l e i n both s t r a i g h t and curved approach

cond i t ions i s t h e Star, ye1 lowlsteady incandescent marker.

10. I f ac tua l t r a i n operat ions w i l l i nvo lve an observer f i r s t

de tec t ing a rear-end t r a i n marker w i t h per iphera l v i s ion , i t

may be most e f f e c t i v e t o use a ye l l ow marker such as t h e S ta r

( f o r g reater br ightness than Star red provides) , bu t inc lude

b l i n k t o provide a t ten t ion-catch ing v i sua l motion f o r an

observer who may be d i s t r a c t e d by o ther dut ies.

This f i e l d t e s t was conducted under near i d e a l environmental

and observer condi t ions. It i s most p roper l y considered a

basel ine comparison o f a sample o f rear-end t r a i n markers.

Ef fect iveness o f t h e markers under vary ing cond i t ions o f

atmospheric t ransmissi b i 1 i t y (fog, r a i n , snow), d i r t bu i ldup on

t h e lens o f t h e markers, obscurants on t h e cab windshield,

c l u t t e r i n t h e v i sua l f i e l d , and/or h igh work load on t h e

observer were no t evaluated. These were considered t o be

outs ide t h e t ime and budget resources o f t h i s cont rac t .

Under t h e cond i t ions o f t h e t e s t , a1 1 markers are acceptable

from t h e standpoint o f t h e v i sua l performance c r i t e r i a

mentioned above. This suggests other, non-vi sual , c r i t e r i a be

used f o r d i s t i n g u i s h i n g among markers, i f necessary. These

c r i t e r i a might inc lude cost , r e l i a b i l i t y , a v a i l a b i l i t y , and

mainta inabi 1 i t y . A1 t e r n a t i v e l y , t he r e s u l t s suggest t h a t

several d i f f e r e n t designs o f rear-end t r a i n markers w i l l be

acceptable from a human fac to rs standpoint.

v i i i

F i n a l Report

REAR-END TRAIN MARKER LIGHT EVALUATION (Contract No. DTFR53-86-C-00006, Task Order No. 7)

1 -0 INTRODUCTION

Beginning i n January 1977, t h e Federal Rai 1 road Admin is t ra t ion (FRA) has requ i red r e a r end marking devices mounted on t h e l a s t c a r o f a l l f r e i g h t

t r a i n s . The purpose o f t h e regu la t i on i s t o mark c l e a r l y t h e l a s t ca r t o pro-

v ide a means f o r prevent ing rear-end c o l l i s ions . The regu la t i on i s pub1 ished

i n t h e Code o f Federal Regulations (CFR) , Par t 221, "Rear End Marking Device - Passenger, Comnuter and Fre igh t Trains". The most app l icab le p a r t o f t h a t

regu la t i on under paragraph 221.14, "Marking Devices", s ta tes , i n par t :

(a) "As prescr ibed i n Sect ion 221.13, passenger, commuter and f r e i g h t t r a i n s s h a l l be equipped w i t h a t l e a s t one marking device which has been approved by the Federal Ra i l road Administrator. . .and which has the f o l 1 owing cha rac te r i s t i cs :

(1) An i n t e n s i t y o f no t l ess than 100 candela no r more than 1,000 candela ( o r an e f f e c t i v e i n t e n s i t y o f n o t l ess than 100 candela n o r more than 1,000 candela f o r f l a s h i n g l i g h t s ) as measured a t t he center o f t h e beam width;

(2) A ho r i zon ta l beam w i t h a minimum arc w id th o f f i f t e e n (15) degrees each s ide o f t h e v e r t i c a l center l i n e , and a ver- t i c a l beam w i t h a minimum arc w id th o f f i v e (5) degrees each s ide o f t h e ho r i zon ta l center l i n e as def ined i n terms o f t h e 50 candela i n t e n s i t y po in ts .

(3) A c o l o r defined by t h e red-orange-amber c o l o r range; and,

(4) I f a f l a s h i n g l i g h t i s used, a f l a s h r a t e o f no t l ess than once every 1.3 seconds o r more than every 0.7 seconds."

E f f e c t i v e i n t e n s i t y i s def ined i n p a r t 221.5(h) as "...that

i n t e n s i t y o f a l i g h t i n candela as def ined by the I l l u m i n a t i n g Engineering

Soc ie ty 's Guide f o r Ca lcu la t ing t h e E f f e c t i v e I n t e n s i t y o f F lashing Signal

L igh ts , November 1964."

To meet this standard, FRA approval of a1 1 rear-end marking devices

is required. The requesting railroad must certify in writing, signed by the Chief Operating Officer, that among other things:

"The device described in the submission (i .e., certification) has been tested in accordance with the current "Guidelines for Testing of FRA Rear End Marking Devices".

In Section 2.1.1 of the Guidelines, photometric tests are required to meet the intensity limits for an on-axis source candle power of

between 100 and 1,000 candela (cd) . For the off-axi s (defined as *15 degrees

horizontally, i 5 degrees vertically), photometric tests must meet a source

candle power between 50 and 1,000 cd. The output is determined with a

suitable photometer. It should have an integrating mode to measure effective

intensity of flashing or strobe lights.

The FRA allows both steady and flashing lights to be used. The

intensity measurement for a steady light is a straightforward measurement of

the peak intensity of the source (marker lamp) at a fixed distance (not less

than 10 ft). For the flashing light, however, the intensity must be inte-

grated across the flash period to compensate for the "apparent" brightness to

the eye being less than its peak intensity. This sample integration is

usually done with a calibrated filter in front of the photometer.

A1 1 rear end marker 1 ights unti 1 very recently were incandescent

bulbs of almost identical design. However, with the advent of the cabooseless

train and battery-powered end-of-train devices , new techno1 ogy using 1 ow-power LED and xenon flash tube lights were developed. Often these devices were

designed to take advantage of the on-axis light intensity requirements. This

could result in an asymmetrical light distribution of uncertainty in the

spread of 1 ight beyond &15 degrees horizontal ly, i 5 degrees vertical ly. This

research project will help resolve these uncertainties with the new rear end

marker light designs.

3

2.0 TEST OBJECTIVE

The objective of the tests under Task Order #7 was to evaluate a

number of new rear end marker lights under both laboratory and field test

conditions. Rear end marker lights of various designs, including incan-

descent, LED, and xenon flash tube, were obtained from four different manu- facturers. Laboratory tests were then conducted to quantify the 1 ight performance. Procedures outlined in the -"Guidelines for Testing of FRA Rear

End Marking Devices" dated November 1977 were used as a basis for the labora-

tory tests. Photometric intensity, flash rate and color were measured for

each device. Field tests were then conducted to assess the visibility to

human observers of the sample of rear-end train marker designs.

3.0 LABORATORY MEASUREMENTS

Two types of measurements were made on the test lamps: relative

spectral i 1 luminance and angular luminous intensity. A 1 ist of the equipment used is given in Table 3-1, and a picture of the goniometer setup is shown in

Figure 3-1. The test lamps are described in Table 3-2. For the three sets of

lights requiring external power, 1 meter long 18 gauge stranded copper leads

were used to minimize current-related ( I R ) voltage drops. The Pulse lamps

were specified and run at 12.60 volts d.c. The DSL and STAR lamps were not

specified and were run at 12.00 volts d.c.

The spectral measurements were relatively'straightforward. The

monochromator was set up to average over 3 or 4 pulses uniformly throughout

the scan. The system was calibrated against the standard lamp to correct for

any spectral bias. Chromaticity coordinates were computed by convolving the

spectrum with the X, Y, Z tristimulus curves. The angular intensity measurements were a bit more involved. Two

sets of measurements, horizontal and vertical, were made for each light at

distances of 25 feet and 100 feet. For horizontal measurements the lamp was

placed upright on the goniometer. Data was taken from -18 to +18 degrees

every 1 degree and thereafter to ~ 9 0 degrees every 5 degrees. For vertical

TABLE 3-1. EQUIPMENT USED IN LABORATORY EXPERIMENTS

Manufacturer Type Model Number Seri a1 Number

Spectral Measurements : EG&G Intel 1 igent Radiometer GS4100 BS 329 EG&G Monochromator NM3 DM GV 558 EG&G Photomul tip1 ier Detector D46CQ PB9467

Luminance Measurements : EG&G Photomul tip1 ier Detector Assembly 2020-10 273 EG&G High Efficiency Photometric Tele- 2020-31 120

scope

Cal i brat i on Standard : EG&G Lamp Monitor and Control RS3 MK1048 EG&G Spectral Radiance Head RSlOA ML994

49 fc 2.5% @ 25 cm 2851°K

Test Lamp Power Supply: Sorensen 1600 watt SRL 60-17 189

Osci 1 losco~e: Tektronix 2430 8012349

Digital Multi-Meter: Fluke ( -01%)

FIGURE 3-1. PHOTOGRAPH OF TEST SETUP

TABLE 3-2. DESCRIPTION OF REAR-END MARKER DEVICES

Manufacturer Lamp Model Ser ia l Number Lamp Type, Ref lec tor Assembly

Dynamic Sciences Ltd. HVM30 1 -OOF 2957, 2981, 2992 Xenon f l ash tube, non-diffused High V i s i b i l i t y Marker parabol i c r e f 1 ector , amber

f i l m on ins ide o f glass cover.

Star Headlight & 845 F Amber (2) Y1, Y2 11156 Bulb, amber o r red Lantern Co. 845 F Red (2) R1, R2 p l a s t i c Fresnel -type lenses.

Pulse Electronics, Inc Tra in l ink HVM L ight 203, 204, 205 Two perpendicular arrays o f high-power red LED'S, w i th a cy l i nd r i ca l Fresnel lens over each array. No f i 1 t e r .

Transi t Control Systems- 5390 End o f Train Marker Xenon f l ash tube w i t h c l ea r 84-1160-101 (2) 102, 104 p l a s t i c d i f f u s e r o v e r i t , a n d 84-1160-102 (1) 103 red o r amber p l a s t i c Fresnel

lens over a1 1.

measurements t h e lamp was placed on i t s s ide on t h e goniometer. The sense o f

t h e measurements, r i g h t , l e f t , above, and below shows where t h e observer would

be r e l a t i v e t o t h e lamp normal. The goniometer has inherent p rec i s ion o f .05

degrees, bu t t h e lamps had t o be mounted t o i t w i t h equal p rec is ion . A

combination of bubble l e v e l s and lase r s igh t ings w i t h m i r r o r s was used t o

ensure tha t :

(1) The t e l ephotometer (TP) was l e v e l ,

(2) The goni ometer base was 1 eve1 on a1 1 axes,

(3) A l i n e normal t o the t e s t lamp f r o n t sur face was c o l l i nea r w i t h t h e TP l i n e o f s igh t .

Bubble l e v e l s were used f o r # I , and 12 as we l l as f o r s e t t i n g t h e

lamp on i t s s ide f o r " v e r t i c a l " measurements. Laser s i g h t i n g was used f o r 83

p rov id ing inherent p rec i s ion o f .0001 degree. However, a m i r r o r was used on

t h e lamp i t s e l f f o r t h i s pa r t , and p o s i t i o n i n g t h e m i r r o r was r a t h e r d i f f i c u l t

f o r some lamps. From t h e p i c t u r e s o f t h e lamps given i n Figures 3-2 through

3-5, i t can be seen t h a t no t one i s s i m i l a r another and none had a standard

mount o r method o f attachment. Some had no obvious attachment f i x t u r e a t a l l

and most had no t r u e f l a t sur face which could be used as a reference f o r

pos i t ion ing . However, a method was developed f o r each type and maintained a t

both 25 f e e t and 100 fee t :

DSL lamps: Front g lass window used as reference surface.

Pulse 1 amps: Cyl i n d i c a l Fresnel 1 ens used as reference.

STAR lamps: Back o f lamp used as reference, l i n e s scr ibed on back w i t h a square f o r v e r t i c a l pos i t i on ing .

TCS lamps: Shroud over lense used as reference w i t h a f l a t s t e e l p la te .

The ac tua l i n t e n s i t y measurements were i n d i r e c t . The standard 1 amp,

c a l i b r a t e d i n terms o f i l luminance a t a given distance,

. was used t o generate a

c a l i b r a t i o n constant f o r t h e t e l ephotometer (TP) At a c e r t a i n h igh voltage,

w i t h t h e standard lamp completely i n s i d e t h e TP f i e l d o f view, a constant was

obtained r e l a t i n g t h e TP anode cur rent - re la ted vol tage ( I R ) drop across a

FIGURE 3-2. DYNAMIC SCIENCES LIMITED

FIGURE 3-3 PULSE ELECTRONICS, INC -

FIGURE 3-4. STAR HEADLIGHT AND LANTERN COMPANY

FIGURE 3-5. 'TRANSIT CONTROL SYSTEMS

known impedance to the illuminance at the TP entrance pupil. The illuminance from the standard lamp, at a distance r is given by:

where Es is the calibrated source illuminance, and d is the distance at which

E is specified. The illuminance of the test lamps at a known distance was the

actual quantity measured. The luminous intensity was inferred from the

following relations. Illuminance is defined by:

where lm are the lumens passing through the area. In this case, the area is just the area of the TP entrance pupi 1 (its 1 imiting aperture).

E = lm/(pupil area) (3-3)

The desired quantity, 1 uminous intensity, I (candlepower) is given by:

where 1m are the lumens contained in the solid angle sr, defined by sr = 2 (measurement area) / (di stance to measured area) . Here the measurement area is

the area defined by the TP entrance pupil and the distance is the distance

from the test lamp to the TP entrance pupil, so that:

= 1m (distan~e)~/(~u~il area) = E (distance)* (3-5)

For example, a calibration constant was obtained for one set of

conditions. The calibration source illuminance was measured at 17 feet 2

inches (523 cm). The signal level = 820 pV, with a neutral density filter =

1.88. The actual illuminance was calculated from the calibration value of 49

11

foot-candles (fc) at 25 cm. The square of the ratio of the measurement distance to the calibration distance is (523125)~ = 438, so that:

E at 17 feet 2 inches = 491438 = 0.112 fc

Then the calibration constant for this set of conditions equals:

Then the DSL f2957 lamp measured on axis, horizontal, at 26 feet with a neutral density filter = 4 and with 106 mV output would be:

(measured output) (f i 1 ter coefficient) (distance)/ (cal . constant)

= (106 mV) (lo4) (26 ft)' /(555 mV/fc) = 1.29(10)~ candela.

4.0 LABORATORY RESULTS

4.1 Test Data

There are two major sections of data: spectral data and intensity

data. The spectral data include the lamp spectrum taken from 380-780 milli-

microns (nanometers) and normal ized to its maximum value. The chromaticity

coordinates are sumnarized in Table 4-1. Plots on linear and log scales are

included in Appendix A for each lamp. The intensity data have two sections, one for 25-foot data and the

other for 100-foot data. A1 1 measurements were made from the peak of the waveform on a high-speed oscilloscope. Sample waveforms are shown in Figures

4-1 through 4-4. A summary of lamp pulse widths, periods, and duty cycles is

given in Table 4-2. Once again, linear and logarithmic plots are given for

each lamplorientation in Appendix B for 25-ft measurements, and in Appendix C for 100-ft measurements. There are four additional plots for the Pulse lamp

TABLE 4-1, S W R Y OF 1931 AND 1 9 7 6 C I E CHROMATICITY COORDINATES

Lamp

DSL 2957 2981 2992

PULSE 203 204 205

STAR R 1 R2 R2S Y 1 Y 2 Y2S

TCS 102 103 104

FIGURE 4-1. DSL LAMP #2957 AT 0 DEGREES

FIGURE 4-2. PULSE LAMP 1 2 0 5 AT 0 DEGREES

FIGURE 4-3. STAR I M P Y2 AT 0 DEGREES

FIGURE 4-4. TCS LAMP #I02 AT 0 DEGREES

TABLE 4-2. SUMMARY OF LAMP DUTY CYCLES

Lamp Pulse Width Pulse Per iod

1.150 sec 1.150 1.145

PULSE 203 204 205

STAR R 1 R2 Y 1 Y 2

TCS 102 103 104

#203, two for 25 feet, the others for 100 feet. They show the intensity profile through the cross pattern for both legs at varying off-axis locations. This was not done for the other lamps because they are spherically symmetric. The sketch in Figure 4-5 shows where the measurenients were made.

Peak and effective intensities are given in Tables 4-3 through 4-6 for the different manufacturers' rear-end marker samples. For the xenon flashlamp type samples (DSL and TCS), Formula 3-28 of the 1978 IES Lighting Handbook (Formula 2-22 of the 1966 version) was used. For the longer pulse- duration lamps, Formula 3-27 (2-21 for 1966) was used. Both formulas involve integra-ting the pulse to obtain pulse energy. Since the pulse shapes for lamps of identical design were similar, only one representative photograph for the pulse shape for each lamp was reported, Figures 4-1 through 4-4. Absolute differences in pulse duration are shown in Table 4-2. A planimeter was used to integrate the pulse for each lamp type. That lamp constant was then scaled by the peak height, obtained from the 100-ft intensity distribution data, and the given pulse duration from Table 4-2.

4.2 Observations

Although measurements were proposed at 10 feet and 100 feet, early data on the Pulse lamps (they were received first) showed that the 11~' relation did not hold true. The 10 feet data were too high when compared with the 10O0 feet data. Presuming that the presence of the cylindrical lens in front of the diodes was disrupting the point source approximation at 10 feet, subsequent measurements were made at 25 feet nominally.

The quantity luminous intensity should be constant for any lamp at any distance, assuming the lamp resembles a point source. Comparing the 25

and 100 feet data for each lamp shows that maximum peak intensities differ non-systematically by approximately 15 percent. Significant sources for this error are as follows:

FIGURE 4-5. IDEALIZED INTENSITY PROFILE OF PULSE LAMP 4203 FROM OBSERVER' S VIEW SHOWING EXTRA HEASURMENTS

Intensity versus horizontal position

-6 0 6 . . . . . -3 3

. . . . .

+30degrees

+20 degrees

I

-20 degrees

Intensity versus vertical position

-10 degrees

TABLE 4-3. INTENSITY VALUES FOR DSL REAR-END MARKERS

49CFR 121 Specif i - Lamp Tested Device Number cat ion L imi t Value

Orientat ion Value # 1 f 2 rOr3 Minimum Maximum

H-v pea ka

~ f f ." 1 . 3 ( 1 0 ) ~ .94(1016 1 . 6 ( 1 0 ) ~ 100 1,000

180 116 203

H-15"R Peak .29(1016 . 2 7 ( 1 0 ) ~ .33(1016 50 1,000

Eff. 40 33 4 3

H-15" Peak .25(1016 . 2 4 ( 1 0 ) ~ . 2 9 ( 1 0 ) ~ 50 1,000

Eff. 3 5 30 3 8

V-5"U Peak .25 (10) .30 (10) .28 (10) 50 1,000

Eff. 3 5 3 7 3 7

V-5"D Peak .23(1016 . 2 4 ( 1 0 ) ~ . 2 7 ( 1 0 ) ~ 50 1,000

Eff. 32 30 3 5

Note: H - V i s defined as the geometrical horizontal/vertica7 center.

a -- Peak intensi ty i n candela;

b -- e f f e c t i v e intensi ty i n candela-seconds.

TABLE 4-4. INTENSITY VALUES FOR PULSE REAR-END MARKERS

49CFR 121 Specif i - Lamp Tested Device Number cat ion L imi t Value

Orientat ion Val ue # l 52 $3 Mi nimum Maximum

H-V peaka 112 107 130 100 1,000

~ f f .b 46 55 67

H-15OR Peak 49 6 4 27 E f f . 20 33 14

H-15" Peak 4 5 5 3 30

E f f . 19 2 7 15

V-5"U Peak 52 49 66

E f f . 2 2 25 3 4

V-5OD Peak 48 4 1 6 0

E f f . 2 0 2 1 3 2

Note: H-V i s defined as the geometrical horizontal / ve r t ica l center.

a -- Peak intensi ty i n candela;

b -- e f f e c t i v e intensi ty i n candel a-seconds.

TABLE 4-5. INTENSITY VALUES FOR STAR REAR-END MARKERS

49CFR 121 S p e c i f i - Lamp Tested Device Number c a t i o n L i m i t Value

O r i e n t a t i o n Value #l 52 #3 Minimum Maximum

RED LENSE

H - V peaka 142 153

~ f f .b

Peak

E f f .

Peak

E f f .

Peak

E f f .

Peak 80 8 0

E f f . 39 38

AMBER LENSE

H-V peaka 475 315

~ f f .b 219 154

H-15"R Peak 175 170

E f f . 8 1 83

H-15" Peak 160 140

E f f . 74 6 9

v-5"U Peak 230 205

E f f . 106 100

V-5"D Peak 240 170

E f f . 11 1 100

Note: H - V i s de f i ned as t h e geometr ica l h o r i z o n t a l / v e r t i c a l cen te r .

a -- Peak i n t e n s i t y i n candela;

b -- e f f e c t i v e i n t e n s i t y i n candela-seconds.

2 1

TABLE 4-6. INTENSITY VALUES FOR TCS REAR-END MARKERS

49CFR 121 S p e c i f i - Lamp Tested Device Number c a t i o n L i m i t Value

Or ien ta t i on Value -- # l C -- #2d -- #3C Minimum Maximum

H - V peaka 1910 7400 1850 100 1,000

~ f f .b .27 .98 .27

H-15OR Peak 1800 6500 1750

E f f . .26 .86 .25

H-15" Peak 1950 7200 1980

E f f . .28 .95 .28

V-5O U Peak 2040 6600 1950

E f f . .29 .87 .28

V-5OD Peak 1910 6600 1950

E f f . .27 .86 .25

Note: H - V i s def ined as the geometr ical ho r i zon ta l / v e r t i c a l center .

a -- Peak i n t e n s i t y i n candela;

b -- e f f e c t i v e i n t e n s i t y i n candela-seconds.

c -- red lens

d -- amber lens

Electronic

(1) Random noise associated with photomultiplier used in TP.

(2) Fluctuations in test lamp electronics, changing lamp output.

Optical

(1) Uncertainty in precise value of neutral density filters used to keep TP out of saturation (f i 1 ters are wavelength dependent)-.

Of these sources, the test lamp fluctuations could be observed directly. Pulses were observed in real time on the oscilloscope and a cursor was set by hand on the peak. Both DSL and TCS, and to a lesser extent Pulse, showed variations in peak heights. The xenon flash tube lamps appeared cyclical with a very strong peak being followed by a very weak one, then increasing to an intermediate peak. The difference between strong and weak was as high as 20 percent.

The values of neutral density were determined individually for each 1 amp type to compensate for wavelength dependence. The error involved was 55 percent when using the standard lamp (white 1 ight) , but 1 ight output fluctu- ations already mentioned complicated determining the filter value for the xenon lamps. Repeated measurements were made to generate average values for peak intensity, enabling filter values to be determined to S10 percent.

The data show positioning accuracy and repeatability was excellent. Intensity profiles for 25 feet match very closely those for 100 feet, with one exception. The vertical measurement for Pulse #204 appears to have been misaligned by several degrees. The profile is correct but the absolute

position is off.

4.3 Comparison with ETL Test Results

As part of their FRA qualification, the manufacturers had an inde- pendent commercial laboratory -- ETL Testing Laboratories, Inc., of Cortland, NY -- test five of each device. In comparing the ETL intensity measurements with Battelle's results, the FRA found that ETL's intensity numbers, both peak

(where g iven) and e f f e c t i v e , were c o n s i s t e n t l y h igher . Th i s i s shown i n Table

4-7 . The FRA, ETL and B a t t e l l e j o i n e d i n an e f f o r t t o r e s o l v e these

d iscrepancies.

The f o l l o w i n g s i g n i f i c a n t d i f f e r e n c e s were es tab l i shed between

B a t t e l l e t s and ETL's t e s t methodologies:

(1) D i f f e r e n t methods o f mount ing t h e dev ices were used. They

were, i n most cases, d e l i v e r e d bo th t o B a t t e l l e and ETL w i t h o u t

p roper mounting surfaces. B a t t e l l e es tab l ished p r a c t i c a l

r e fe rence p lanes f o r each, us i ng t h e nominal geometr ic c e n t e r

and ma in ta i n i ng t h i s f o r bo th 2 5 - f t and 1 0 0 - f t measurements.

ETL searched f o r t h e "ho t spo t " ( p o i n t o f h i ghes t i n t e n s i t y ) ,

which does n o t necessa r i l y c o i n c i d e w i t h t h e geometr ic cen te r .

(2) B a t t e l l e used d i f f e r e n t vo l t age e x c i t a t i o n s than ETL used f o r

severa l o f t h e devices. When t h e vo l t age was n o t s p e c i f i e d ,

B a t t e l l e used 12.0 v o l t s f rom a regu la ted power supply. ETL

may have used up t o 0.8 v o l t h i g h e r e x c i t a t i o n . From prev ious

measurements o f locomot ive h e a d l i g h t i n t e n s i t i e s a t 30 and 22

v o l t s , t h e i n t e n s i t y v a r i e d as t h e 4th power o f t h e vo l t age

r a t i o .

(3) Some o f t h e t e s t e d u n i t s were d i f f e r e n t s e r i a l numbers, even

d i f f e r e n t model numbers (a l though these were s a i d t o be t h e

same bas i c u n i t s ) . Some o f t h e u n i t s were d e l i v e r e d t o

B a t t e l l e w i t h d i f f e r e n t candlepower bu lbs f rom t h e ETL u n i t s .

(4) I t was noted t h a t , p a r t i c u l a r l y w i t h t h e f l a s h tube dev ices, a

r a t h e r l a r g e var iance i n pu l se peak i n t e n s i t y ( f rom pu l se t o

pu lse) was observed. Th i s va r i ance was g i ven as *10 percen t

f o r t h e DSL lamp.

Other aspects o f t h e measurements -- t h e shape and d u r a t i o n o f

scope-recorded pulses, and t h e c h r o m a t i c i t y coord ina tes -- checked c l o s e l y

f rom one l a b o r a t o r y t o t h e o ther .

I n o r d e r t o determine t h e cause o f t h e d i f f e r e n t i n t e n s i t y values,

B a t t e l l e s t a f f t r a v e l e d t o t h e ETL l a b o r a t o r y t o compare s tandard sources and

t o measure t h r e e o f t h e rear-end marker dev ices w i t h bo th se t s o f equipment.

TABLE 4-7. COMPARISON OF REAR-END MARKER LIGHT INTENSITY TEST RESULTS

Pulse Tested U n i t s Ave. Peak I (cd) Ave. E f f . I (cd-s)

Mfg . Type o f Device Width BCD ETL B a t t e l l e ETL B a t t e l l e ET L

DSL Xenon f l a s h tube 17 ps 3 5 1 . 3 ( 1 0 ) ~ n a 166 29 1

Star Incandescent lamp, red 255 msec 2 5 148 525 cw 7 1 2 48

, amber 253 msec 2 5 395 n a 187 538

Pulse LED ar ray 238 msec 3 5 116 n a 56 128

TCS Xenon f l a s h tube, red 25 ps 2 5 1880 3 120 0.27 n a

, amber 25 ~s 1 5 7400 10100 0.98 n a

Note: E f f e c t i v e i n t e n s i t y i s ca lcu la ted by i n t e g r a t i n g over t he pu lse and us ing t h e appropr iate IES formula.

The standard sources were compared f i r s t . B a t t e l l e ' s telephotometer was c a l i -

b ra ted f i r s t w i t h i t s source, and then w i t h ETL's source. Our reading was 1.9

percent h igh r e l a t i v e . t o t h e ETL c a l i b r a t i o n data. Next, t h e B a t t e l l e equip-

ment, which had been c a l i b r a t e d a t 25 f e e t , was moved t o 50 and 100 f e e t . A t

each l o c a t i o n the reading was 11 percent low. This discrepancy remained con-

s t a n t regardless of t h e source. We concluded t h a t t h e r e t i c l e eyepiece image

plane on t h e telephotometer was not confocal w i t h the f i e l d s top image plane.

This caused t h e image a t t h e f i e l d stop t o be out o f focus and the i n t e n s i t y

reading t o be low. Our o r i g i n a l data d i d no t e x h i b i t t h i s problem, bu t t he

equipment had been heav i l y used s ince these measurements were made and must

s ince have become misal igned. Since the e r r o r was r e l a t i v e l y smal l , t he com-

p a r a t i v e t e s t i n g was continued.

The th ree rear-end marker devices were then measured a t 100 f t w i t h

the same equipment used prev ious ly . Since the c a l i b r a t i o n was done a t 25 ft,

the r e s u l t s were expected t o be 11 percent lower than ETL's. ETL's system f o r

mounting and p o i n t i n g the devices was used, and the measurements were made

very c lose t o t h e l o c a t i o n used by-ETL. Resul ts o f these measurements are

summarized i n Table 4-8 and compared w i t h subsequent measurements on t h e th ree

devices made by ETL w i t h t h e i r equipment. With the except ion o f t he Star

lamp, t h e r e s u l t s a re q u i t e s i m i l a r . ETL noted t h a t i n t e s t i n g t h e S ta r lamp,

t he mounting was loose, and a s l i g h t s h i f t could r e s u l t i n d i f f e r e n t measured

values.

Based on these comparative t e s t s , i t appears t h a t t he d i f f e rences i n

mounting techniques account f o r t he major d i f f e rences i n measured i n t e n s i t y .

The recommended approach t o avoid these d i f f e rences i s t o r e q u i r e the device

manufacturer o r app l i can t t o supply a mounting base o r t e s t stand t o i nsu re

proper alignment dur ing t e s t i n g . Since devices are a lso occas iona l l y sub-

m i t t e d i n p ro to type form, t e s t s should be requ i red on product ion-run devices

t o assure compl i ance w i t h FRA requirements.

TABLE 4-8. COMPARISON OF LIGHT INTENSITY MEASUREMENTS UNDER SIMILAR TEST CONDITIONS

E f f e c t i v e I (cd-s) Previous

Dev i ce Di f fe rences from Previous Tests Peak I (cd) B a t t e l l e ETL Data

DSL #2957 Same u n i t as tes ted (Device #1) 1.23(10)~ 23 4 252 180

STAR #I089 D i f f e r e n t bezel and r e f l e c t o r 304 164 224 187

TCS #I56 D i f f e r e n t u n i t 1.12(10)~ 1.11 0.97 0.98 N (TI

Note: E f f e c t i v e i n t e n s i t y i s ca lcu la ted by i n t e g r a t i n g over t he pu lse and us ing t h e appropr iate I E S formula.

27

5.0 FIELD EXPERIMENTS

As a second phase t o t h i s program, a f i e l d t e s t was conducted t o

assess t h e v i s i b i l i t y o f t h e sample rear-end t r a i n markers. Experiments were

designed t o t e s t t h e c o n s p i c u i t y o f markers d i f f e r i n g i n lamp type, c o l o r ,

1 i g h t c y c l e (pu lse versus steady), and luminance. A fundamental i s s u e i s

whether human observers (i .e., locomot ive engineers) can adequately d e t e c t t h e

markers when approaching t h e end o f another t r a i n on e i t h e r tangent o r curved

t r a c k .

Tangent- track approaches i n v o l v e on-ax is v iew ing o f a marker. On

t h e o t h e r hand, cu rved- t rack approaches i n v o l v e o f f - a x i s v iew ing o f a marker,

t h e degree o f which depends on how curved t h e t r a c k i s and t h e l o c a t i o n o f t h e

human observer r e l a t i v e t o t h e marker l i g h t a t any p o i n t i n t ime. The FRA has

suggested t h a t , t o i n s u r e s a f e t y under c o n d i t i o n s o f a s low approach a t 15

mph, a human observer should be ab le t o see a rear-end t r a i n marker 1 i g h t such

t h a t a t l e a s t one thousand f e e t (1000') o f t r a c k s topp ing d i s tance remains

when d e t e c t i o n occurs.

The o b j e c t i v e o f t h i s f i e l d t e s t was t o assess t h e v i s i b i l i t y t o

human observers o f a sample o f rear-end t r a i n marker designs. A v a r i a t i o n o f

best -caselworst -case a n a l y s i s was employed i n t h e f i e l d t e s t . The t e s t i n g

i nvo l ved an on-axis v iew ing c o n d i t i o n which represen ts t h e "bes t case" f o r

1 i g h t s designed t o t ake advantage o f on-axi s 1 i g h t i n t e n s i t y requi rements.

The o f f - a x i s v iew ing c o n d i t i o n , s i m u l a t i n g an approach on a curved t r a c k ,

represen ts t h e "wors t case" f o r l i g h t s designed p r i n l a r i l y t o emphasize on-ax is

1 i g h t i n t e n s i t y . Th i s f i e l d t e s t used bo th s u b j e c t i v e assessments and v i s u a l

d e t e c t i o n performance t o assess a sample o f e i g h t d i f f e r e n t rear-end t r a i n

marker l i g h t s p rov ided t o B a t t e l l e by t h e manufacturers. The e i g h t samples

were chosen f rom t h e markers i n t h e p rev ious pho tomet r i c eva lua t i ons : one

dev ice f o r each manufacturer (two, i f bo th amber and r e d lenses were sub-

m i t t e d ) , p l u s pu lsed and s t e a d y - l i g h t c o n d i t i o n s f o r t h e S t a r lamps.

5.1 Experimental Background

The Federal Rai 1 road Admin i s t r a t i on (FRA) has i n d i c a t e d t h a t r e a r -

end markers should be d e t e c t i b l e such t h a t , assuming a s low approach a t 15

mph, t h e r e i s a t l e a s t 1000' o f t r a c k s topp ing d i s tance a v a i l a b l e t o t h e

locomot ive engineer upon d e t e c t i n g t h e marker o f another parked o r slow-moving

t r a i n . Th i s 1000' c i r c u l a r (s topping) d i s t ance imp1 i e s t h a t markers should be

d e t e c t i b l e a t a v iew ing angle, 0, o f 1 r a d i a n (57.3') o r more. (See Appen-

d i x D f o r f u r t h e r exp lanat ion. ) The i m p l i c a t i o n o f t h i s r e s u l t i s t h a t any

rear-end marker which i s v i s i b l e a t an angle o f 57.3' o r g r e a t e r i s acceptable

f rom t h e s tandpo in t o f human v i s u a l performance. I n such a case, o t h e r c r i -

t e r i a such as cos t , m a i n t a i n a b i l i t y , r e l i a b i l i t y , e tc . , cou ld be used t o

choose f rom among severa l products . A l t e r n a t i v e l y , t h e i m p l i c a t i o n i s t h a t

severa l products a r e s a t i s f a c t o r y f rom t h e s tandpo in t o f human v i s u a l perform-

ance.

The geometry o f t h e curved t r a c k approach suggested an a l t e r n a t i v e

methodology which would o b v i a t e t h e need t o use a curved t r a c k f o r da ta

c o l l e c t i o n . The l o g i c o f t h i s a l t e r n a t i v e methodology i s g iven below. As

i n d i c a t e d i n F igu re 5-1, as an observer t r a v e l s around a curve and approaches

a t r a i n marker, t h e angle e between t h e marker ' s e m i t t e r l i n e and t h e obser-

v e r ' s l i n e o f s i g h t grows sma l l e r and t h i s 'exposes' more o f t h e marker t o t h e

observer. The angle e, then, determines t h e marker ' s de tec t i on . Th i s angle

can a l s o be d i r e c t l y r e l a t e d t o s topp ing d is tances . Given these r e s u l t s ,

i n s t e a d o f t e s t i n g w i t h a s t a t i o n a r y marker and a moving observer, i t was

p o s s i b l e t o conduct a s i m u l a t i o n w i t h a s t a t i o n a r y observer and a moving

marker. s p e c i f i c a l l y , an observer was s i t u a t e d a t a f i x e d d i s t a n c e o f 1000'

f rom a marker seated on a t u r n t a b l e . A t r i a l s t a r t e d w i t h an ang le o f more

than 90' between t h e marker ' s e m i t t e r l i n e and t h e obse rve r ' s l i n e o f s i g h t so

t h e observer cou ld n o t see t h e marker a t t h e o u t s e t (hence t h e term " o f f - a x i s "

v iew ing c o n d i t i o n ) . The marker was then r o t a t e d s l o w l y toward t h e observer

u n t i l t h e observer s i gna led t h a t he/she de tec ted t h e marker. The d e t e c t i o n

ang le was recorded as t h e dependent v a r i a b l e f o r each o f t h e markers and used

t o assess t h e e f f e c t s o f va r ious markers on t h e a b i l i t y o f human observers t o

see them. By v i r t u e o f t h e s imu la t i on j u s t descr ibed, i f a marker was

de tec ted by, say, r o t a t i n g a marker ( w i t h respec t t o a s t a t i o n a r y observer) t o

EMlllER LINE REAR-END

OBSERVER

FIGURE 5-1. GEOMETRY OF A CURVED-TRACK APPROACH TOWARD A REAR-END MARKER DEVICE

a detec t ion angle o f 85O, t h i s i s analogous t o a moving observer de tec t ing a

s ta t i ona ry marker by moving through an angle o f 90' - 85' = 5' from t h e

s t a r t i n g p o i n t on the opposite s ide o f a c i r c u l a r t rack . Thus, v i sua l performance data were co l l ec ted t o evaluate t h e v i s i b i l i t y o f t h e sample o f

rear-end t r a i n markers. Appendix D conta ins f u r t h e r explanat ion o f t h e

geometry o f curved t r a c k approaches.

Consider nex t a slow approach along a tangent t rack. Previous research f o r t h e FRA on rear-end t r a i n markers (Sherman, Ray, and Meacham,

1984), in formal observat ions made by t h e i nves t iga to rs , and data from a small

p i l o t study conducted f o r t h i s e f f o r t a l l ind ica ted t h a t a detec t ion task was

not f e a s i b l e because a l l o f t he markers were c l e a r l y v i s i b l e a t a d is tance o f

1000' i n t h e on-axis viewing condi t ion. As an a1 te rna t i ve , sub jec t i ve assess-

ments o f marker v i s i b i l i t y were co l l ec ted using both r a t i n g scales and p a i r

comparisons. Detai 1 s o f t h e approach used and r e s u l t s c o l l e c t e d are presented

be1 ow.

5.2 Human Subjects f o r Experiments

The subjects i n t h e f i e l d t e s t inc luded 14 male and 10 female

volunteers o f ages 24 t o 57 years. A l l subjects were screened by B a t t e l l e

Health Services t o insure Snel 1 en a c u i t y o f 20130 o r b e t t e r ( co r rec t i ve 1 enses

were allowed) as measured by a Titmus t e s t i n g device. Subjects were a l so

screened t o insure t h a t subjects exh ib i ted no c o l o r v i s i o n problems as

assessed by means o f t h e I sh iha ra c o l o r p la tes . By d i r e c t i o n o f t h e FRA

techn ica l representat ive, no r a i 1 road personnel o r people w i t h r a i 1 road

experience were inc luded i n the sub jec t pool. This was done t o e l im ina te any

biases regarding preferences o f markers due t o p r i o r exposure t o s i m i l a r types

o f markers. Subjects were pa id $25.00 f o r t h e i r p a r t i c i p a t i o n i n t h e f i e l d

t e s t and signed a sub jec t consent form as requ i red by B a t t e l l e po l i cy . Table

5-1 shows t h e d i s t r i b u t i o n o f t h e subject sample by age and gender.

TABLE 5-1. DISTRIBUTION OF SUBJECTS I N THE FRA REAR-END TRAIN MARKER FIELD TEST BY AGE AND GENDER

Gender Age Ma1 e Fema 1 e Row Total s

Column Totals: 14 10 24

5.3 Experimental Apparatus

5.3.1 Equipment

E ight t r a i n markers were evaluated i n t h i s study. The markers

possessed the fo l low ing character is t ics :

TABLE 5-2. DESCRIPTION OF REAR-END MARKER TYPES AND CONDITIONS

- No. Manufacturer Descript ion Color Cycl e

Star Headlight and Lantern Incandescent Red Pu 1 sed Star Headlight and Lantern Incandescent Red Steady Star Headlight and Lantern Incandescent Ye1 low Pulsed Star Headlight and Lantern Incandescent Ye1 1 ow Steady Pulse Electronics, Inc. LED Red Pul sed Trans i t Control System Xenon Pulse Red Pul sed Trans i t Control System Xenon Pulse Ye1 low Pu 1 sed Dynamic Sciences, Ltd. Xenon Pulse Red Pulsed

The markers were mounted on ac ry l i c bases t o provide s tab le supports

and help i n posi t ioning. For the detect ion task, they were placed on a c i r -

cu la r plywood t u rn tab le which was painted black t o reduce the amount o f

r e f l e c t e d l i g h t . Holes d r i l l e d i n t h e t u r n t a b l e provided s tandard iza t ion of

p o s i t i o n i n g of t h e markers on the tu rn tab le . A 1.8 hp motor, mounted on a

stand beneath t h e t u r n t a b l e prov ided a f i x e d r a t e o f r o t a t i o n (1.25 deglsec,

as shown i n t h e d e r i v a t i o n o f Appendix D, page D-4).

Three battery-powered but ton switches, loca ted a t t he observer s i t e ,

were ac t i va ted by the subjects upon de tec t i on o f t he marker. These switches

were connected, v i a a length o f 1000' mul t i -channel cable, t o t h ree e l e c t r o n i c

counter t imers (Fluke Model 1950A) which recorded the t imes when t h e subjects

depressed t h e i r switches. A dual - regulated power supply connected t o both the

motor and a l l t h ree o f t h e counters prov ided t h e means o f simultaneously

s t a r t i n g t h e t u r n t a b l e r o t a t i o n and a c t i v a t i n g t h e counters. A but ton press

by a sub jec t stopped the appropr iate counter; t h e numeric value d isp layed on

t h a t counter represented detec t ion t ime i n seconds, i.e., t h e t ime t h a t

elapsed between t h e s t a r t o f t u r n t a b l e r o t a t i o n t o de tec t i on o f t h e marker by

t h a t subject . Since t h e degree o f t u r n t a b l e r o t a t i o n was constant, t h e

de tec t i on angle was e a s i l y ca lcu la ted from t h e de tec t i on t ime and a known

s t a r t i n g p o s i t i o n . An extension cord, connected t o an o u t l e t i n a nearby

guard house a t B a t t e l l e ' s West Jef ferson, Ohio, t e s t s i t e , prov ided t h e

necessary AC power f o r t h e power supply and t h e e l e c t r o n i c counters. The

equipment a t t he marker s i t e was se t up on top o f a 38" h igh f o l d i n g t a b l e

which was placed i n t he center o f t he road used f o r t e s t i n g , thus ensuring

f a i r l y cons i s ten t p o s i t i o n i n g o f equipment throughout t h e e i g h t days o f

t e s t i n g .

A 12 -vo l t marine ba t te ry , enclosed i n a c a r r y i n g case f o r ease o f

handl ing, provided the power source f o r s i x o f t he e i g h t markers. The o ther

two markers, (T rans i t Contro l System 1 i g h t s ) had se l f -conta ined power sources.

See Figures 5-2 through 5-6 f o r schematic diagrams and photographs o f t h e

experimental set-up, t e s t s i t e , and arrangement o f sub jec ts dur ing t e s t i n g .

Hand-held two-way rad ios prov ided the means o f communicating between

t h e observer and marker s i t e s , separated by 1000'. I n some instances,

s i g n a l i n g by f l a s h l i g h t s was s u f f i c i e n t t o i n d i c a t e t h e s t a r t o r end o f a

t r i a l .

OBSERVER SlTE

MARKER SlTE

ELll-rON TIMERS SWITCHES -

-0 0 0 0

-0 0 0 .

-0 0 0 0

1000' CABLE

POWER SUPPLY

FIGURE 5-2. SCHEMATIC DIAGRAM OF EQUIPMENT FOR F IELD TESTS

TIMERS POWER SUPRY

FIGURE 5-3. ARRANGMENT OF EQUIPMENT AT MARKER S I T E

FIGURE 5-4. PHOTOGRAPHS OF EQUIPMENT SET UP AT MARKER S I T E

FIGURE 5-5. POSITION OF SUBJECTS DURING TESTING

FIGURE 5-6. EXPERIMENTAL TEST SITE, LOOKING FROM OBSERVER S ITE TOWARD REAR-END MARKER SITE, 1000-FT AWAY

5.3.2 Experimental Design

I n order t o minimize systematic learning and fa t igue e f fec ts , the

subjects were given t r i a l s scheduled according t o the fo l lowing Latin-square:

Sequence o f 4-Tr ia l Blocks

SUBJECT 1 2 3 4 5 6 7 8 NUMBER

Session 1 01, 02, 03 A B C D E F G H 2 04, 05, 06 B C D E F G H A 3 07, 08, 09 C D E F G H A B 4 10, 11, 12 D E F G H A B C 5 13, 14, 15 E F G H A B C D 6 16, 17, 18 F G H A B C D E 7 19, 20, 21 G H A B C D E F 8 22, 23, 24 H A B C D E F G

The codes f o r the markers are as fol lows:

Star lYe l low/Pul sed Pul se/Red/Pulsed TCSIYel 1 ow/Pul sed StarIRedlPul sed Star lYe l lowlsteady TCSIRedlPul sed DSLIRedlPul sed StarIRedlSteady .

5.4 Experimental Procedure

Testing was conducted a t Ba t t e l l e ' s f a c i l i t i e s i n West Jefferson,

Ohio, located approximately 20 mi les west o f Columbus. The t e s t s i t e was a

s t r a i gh t , f l a t sect ion o f road, selected so as t o ensure t ha t a c lea r l i n e o f

s igh t o f 1000' was avai lable, i.e., w i t h no obstruct ions such as bui ld ings,

t rees o r bushes. An addi t iona l requirement was t ha t the t e s t s i t e was dark,

w i th no nearby l i g h t s which would d i s t r a c t o r confuse the subjects. Thus,

nearby secur i t y l i g h t s were extinguished f o r the durat ion o f the experiment.

The s i t e where the markers were placed was selected t o avoid any nearby

objects which might r e f l e c t l i g h t from the markers, thus provid ing secondary

cues as t o the markers' posi t ion. When necessary, dark c l o t h was draped over

r e f l e c t i v e posts and signs i n the v i c i n i t y o f the markers t o e l iminate

unwanted re f lec t ions .

The experimental sessions were scheduled on n i g h t s w i t h no p rec i -

p i t a t i o n ; sk ies var ied from c l e a r t o cloudy. The sessions l as ted between t h e

approximate hours - o f 9:30 and 11:30 p.m. It was f e l t t h a t v a r i a b i l i t y i n t r o - duced by t h e n igh t t ime sk ies was no t a s i g n i f i c a n t f a c t o r i n t h e experiment.

Also, t he re was noth ing t h a t could be done t o con t ro l t h i s fac to r . Subjects

were g iven d i r e c t i o n s and maps t o t h e t e s t l oca t ion , and were informed o f

t h e i r assigned t e s t session. Three subjects were scheduled per t e s t session.

Upon a r r i v a l a t t h e t e s t locat ion , they were greeted by t h e experimenter,

g iven a b r i e f overview o f t h e experimental procedure, and shown t h e marker

l i g h t s and equipment se t up a t t h e marker s i t e . The subjects then entered a

mini-van and were d r i ven t o t h e observat ion s i t e , located 1000 f e e t away from

t h e marker locat ion ; t h e mini-van was then parked and served as t h e

observat ion s i t e . Once a t t h e observat ion s i t e , t he subjects were given a

more d e t a i l e d desc r ip t i on o f t h e experiment. The experiment was conducted i n

th ree phases:

Phase I: V i s i b i l i t y and Glare Rating. The subjects were given

c l ipboards conta in ing t h e data sheets w i t h r a t i n g scales f o r marker v i s i b i l i t y

and g lare. A f t e r they were given i n s t r u c t i o n s on t h i s phase o f t h e

experiment, t h e f i r s t marker was turned on. The marker was located a t t h e

marker s i t e and pos i t ioned so t h a t i t d i r e c t l y faced t h e subjects ( the on-axis

viewing condi t ion) . The marker remained on f o r 15-20 seconds and was then

turned o f f . Dur ing t h i s t ime, t h e subjects looked a t t h e marker, evaluated i t

w i t h respect t o i t s v i s i b i l i t y and g lare, then ind ica ted t h e i r choices on t h e

v i s i b i l i t y and g l a r e scales on t h e data sheet. A f t e r t h e f i r s t marker was

f in ished, i t was replaced by t h e next marker, and t h e process was repeated

u n t i l a l l e i g h t markers had been evaluated.

Phase 11: Detect ion Task, In t h i s phase o f t h e experiment, t h e

f i r s t marker was placed on a tu rn tab le , w i t h t h e face o f t h e marker turned 120

o r 180 deg away from t h e subjects (0 deg represented the p o s i t i o n i n which t h e

marker was d i r e c t l y fac ing t h e subjects) ; s t a r t i n g pos i t i ons were determined

f o r each marker from a p i l o t study. A schematic diagram o f t h e marker s t a r t -

i n g p o s i t i o n r e l a t i v e t o t h e subjects i s given i n F igure 5-7. The marker was

turned on and t h e motor ac t iva ted, causing the marker t o r o t a t e s lowly toward

t h e subjects ( o f f - a x i s viewing cond i t ion) . Each subject he ld a but ton swi tch

OBSERVER SlTE

MARKER SlTE

f TURNTABLE

FIGURE 5-7. MARKER STARTING POSITION, RELATIVE TO SUBJECT

which was t o be depressed when helshe f i r s t saw t h e l i g h t from t h e marker.

They were caut ioned against responding t o r e f l e c t i o n s o f f surrounding ob jec ts

such as t rees, t h e ground, o r signs. Each marker was presented i n a b lock

cons is t i ng o f one p r a c t i c e t r i a l ( t o acquaint t he subjects w i t h t h e marker

c h a r a c t e r i s t i c s ) and th ree t r i a l s used f o r data c o l l e c t i o n . During t h e

p r a c t i c e t r i a l , t h e subjects depressed the but ton switches upon detect ion, but

no data were co l lec ted. An aud ib le c l i c k could be heard when a but ton swi tch

was depressed; thus t h e subjects could be cued as t o when someone e l s e had

detected a 1 i gh t . For t h i s reason, they were caut ioned t o respond honest ly,

i .e., on l y when they had f i r s t detected the 1 i g h t from t h e marker. I f , f o r

some reason, t h e subjects f e l t t h a t they had responded inapprop r ia te l y o r

i n c o r r e c t l y , they informed t h e experimenter, t he t r i a l was declared a m i s t r i a l

(no data recorded), and i t was repeated.

Phase 111: P a i r Comparisons, Pa i rs o f markers were simultaneously

displayed, on-axis, t o t h e subjects, f o r approximately 15-20 seconds. During

t h i s t ime, t h e subjects observed t h e markers, then ind ica ted on a data sheet

which marker o f a p a i r was considered "more v i s i b l e " and "more g lar ing . "

Every marker was compared against a l l o f t he o ther markers i n t h e study,

r e s u l t i n g i n 28 p a i r comparisons. To f a c i l i t a t e ease o f changing t h e markers

being compared, a m a t r i x o f comparisons was devised so t h a t t h e r i g h t marker

of t h e p a i r t o t h e r i g h t o f t h e observers remained constant; t h e remaining

markers were then displayed, i n sequence, as the marker t o t h e l e f t o f t h e

observers. For example, Marker A was placed on the r i g h t side. On t h e l e f t

s ide, Markers B, C, D, E, F, G, and H were displayed i n sequence (one a t a

time.) Next, Marker A was replaced by Marker B on t h e r i g h t side, and t h e

remaining markers (C, D, E, F, G, and H) were displayed on t h e l e f t s ide. The

presenta t ion schedules f o r t h e e i g h t t e s t sessions are shown i n Figure 5-8.

A l l subjects were i n t h e dark f o r a t l e a s t 20 minutes p r i o r t o t h e

s t a r t of t h e o f f - a x i s de tec t ion t r i a l s . I n order t o mainta in t h i s dark

adaptat ion, throughout t h e t e s t session, a l l van l i g h t s were kept o f f .

However, t h e subjects were each equipped w i t h a small pen1 i g h t which was. used

when they recorded t h e i r responses on t h e r a t i n g forms.

CROUP 1: GROUP 5:

A B C D E F C H A - 1 2 3 4 5 6 7 B - 8 9 10 11 12 13 C - 14 15 16 17 18 D - 19 20 21 22 E 23 24 25 F - 26 27 6 - 28 H -

GROUP 2:

B C D E F G H A 8 - 1 2 3 4 5 6 7 C - 8 9 10 11 12 13 D - 14 15 16 17 18 E - 19 20 21 22 F - 23 24 25 G - 26 27 H - 28 A - CROUP 3:

C D E F G H A B C - 1 2 3 4 5 6 7 D - 8 9 10 11 12 13 E - 14 15 16 17 18 F - 19 20 21 22 6 - 23 24 25 H - 26 27 A - 28 B - GROUP 4:

D E F C H A B C 0 - 1 2 3 4 5 6 7 E - 8 9 10 I t 12 13 F - 14 15 16 17 18 6 - 19 20 21 22 H - 23 24 25 A - 26 27 B - 28 C -

GROUP 6:

F G H A B C D E F - 1 2 3 4 5 6 7 G - 8 9 10 11 12 13 H - 14 15 16 17 18 A - 19 20 21 22 B - 23 24 25 C - 26 27 D - 28 E - GROUP 7:

G H A B ' C D E F 6 - 1 2 3 4 5 6 7 H - 8 9 1 0 1 1 1 2 1 3 A - 14 15 16 17 18 B - 19 20 21 22 C - 23 24 25 0 - 26 27 E - 28 F - GROUP 8:

H A B C D E F G H - 1 2 3 4 5 6 7 A - 8 9 I 0 11 12 13 B - 14 15 16 17 18 C - 19 20 21 22 D - 23 24 25 E - 26 27 F - 28 G -

F IGURE 5-8. P A I R COMPARISON PRESENTATION SCHEDULES

-

6.0 FIELD UPERIMENTAL RESULTS AND DISCUSSION

Three types o f measurements were co l l ec ted from the subjects i n t h i s

study. Subjects r a t e d t h e v i s i b i l i t y o f t he markers, one marker a t a t ime, i n

a c o n d i t i o n where they were s i t u a t e d 1000 f t from a marker and viewed t h e

marker on-axis; t h i s simulated a tangent t r a c k (0") approach a t 1000 fee t .

Under t h e same cond i t ions , subjects were a l so presented w i t h a l l unique p a i r s

o f t h e e i g h t markers and were asked t o make a forced-choice pa i red comparison

o f which member o f each p a i r was most v i s i b l e . The sub jec ts ' de tec t i on t imes

du r ing s imulated approaches along an 11.5O curved t r a c k were a l so recorded i n

o rder t o determine angles a t which d i f f e r e n t markers could be f i r s t detected.

The methods o f ana lys i s used and r e s u l t s obtained from t h e data are repor ted

below.

6.1 V i s i b i l i t y Rat ings

A f i v e - p o i n t L i k e r t scale was used t o c o l l e c t t h e v i s i b i l i t y r a t i n g s

from subjects. These r a t i n g s were then tabu la ted t o determine t h e d i s t r i b u -

t i o n o f responses by subjects t o the var ious markers. The v i s i b i l i t y scale

and r e s u l t s a re presented i n Table 6-1.

The f o l l o w i n g propor t ions o f subjects r a t i n g t h e v i s i b i l i t y o f a

g iven marker "Good" o r "Very Good" are repor ted i n Table 6-1:

Marker A (pu lsed lye l low incandescent Star) : p = .833

Marker B (pulsedl red LED Pulse) : p = .625

Marker C (pul sed lye l 1 ow Xenon TCS) : p = .I25

Marker D (pul sedl red incandescent Star) : p = .958

Marker E (steadylye1 low incandescent S tar ) : p = .958

Marker F (pulsedl red Xenon TCS) : p = .I67

Marker G (pulsedl red Xenon DSL) : p = .833

Marker H (s teadyi red incandescent Star) : p = .958.

TABLE 6-1. SUBJECT RATINGS OF REAR-END TRAIN MARKER V I S I B I L I T Y AT 0. 1000 FOOT APPROACH (N = 24).

Marker A Marker V i s i b i l i t y : . . 1 a : 3 : 10 : 10 :

Very Poor : poor-~orderl i ne: Good : Very Good

Marker B Marker V i s i b i l i t y : 4 : 5 : 9 : 6 :

Very Poor : Poor :Border1 ine: Good : Very Good

Marker C Marker V i s i b i l i t y : 9 8 : 4 : 2 : 1

Very Poor : Poor :Border1 ine: Good : Very Good

Marker D Marker V i s i b i l i t y : . . 1 : 12 : 11

Very Poor : Poor :Border1 ine: Good : Very Good

Marker E Marker V i s i b i l i t y : . . . 1 11 : 12 :

Very Poor : Poor :Border1 ine: Good : Very Good

Marker F Marker V i s i b i 1 i ty : 6 1 0 : 4 : 2 : 2 :

Very Poor : Poor :Border1 ine: Good : Very Good

Marker G Marker V i s i b i 1 i ty: . . 4 : 5 : 15 :

Very Poor : Poor :Border1 ine: Good : Very Good

Marker H Marker V i s i b i l i t y : . . 1 : 10 : 13 :

Very Poor : Poor :Borderl ine: Good : Very Good

--

a: Numbers i n d i c a t e t h e frequency o f a given response category by t h e subjects i n t h e f i e l d t e s t .

These proportions are each estimates of the true proportion, 4, in the population of human observers (represented by the subjects) who would rate

a given marker's visibility as "Good" or better. Such an estimate for a proportion may be quite close to that true proportion but wi 1 1 practically

ever actually equal it. This is due to a variety of reasons that collectively

are referred to as sampling error. Because of this, confidence intervals are computed that offer a range of estimated proportion values with a specified

probability (usually -90, .95, or .99) of containing the true population

proportion value. The 95 percent confidence interval (CI) is comnonly used

and has been appl ied to the above data and represented in Figure 6-1. The formula used for these confidence intervals is given by Devore (1982, p. 330)

as :

where + = true population proportion p = empirical proportion 9 ' 1 - p z* = the square of the standard normal deviate for a/2

012 a = 1 - the confidence level, e.g., a = 1 - .95 = .05 n = population number.

6.2 Pair Comparisons o f Visibility

In addition to rating markers one at a time for visibility using the

Li kert scale, subjects were also presented with a1 1 8(7)/2 = 28 unique pairs

of the eight markers, and asked to make a forced-choice comparison of which member of each pair was most visible. This method of pair comparisons has

proven to be extremely useful in human factors engineering because humans are

especially good at making such simple relative judgments (Dunn-Rankin, 1983).

In this field test, the pair comparison procedure produced an 8x8

frequency matrix, F, with Markers A through H as rows and Markers A through H as columns. A cell corresponding to a given row and column of this matrix contained the number of subjects, out of 24, who judged the column marker to

be more visible than the row marker. Elements of the F matrix were then

(95% CI)

FIGURE 6-1. EMPIRICAL PROPORTIONS OF RATINGS FOR V I S I B I L I T Y "GOOD" OR "VERY GOOD", AND 95 PERCENT CONFIDENCE INTERVAL

divided by the total number of subjects and a matrix of proportions, P, was obtained. The matrix P is given in Table 6-2. (Proportions greater than

.98or less than .02 have been rounded .98 and .02, respectively).

Note that the proportions in cell ji and cell ij of the P matrix must sum to 1. Note also the sum of column proportions given below the P

matrix. These sums establish a rank order of visibility for the markers. The rank order of markers in terms of visibility is given here:

Best visibility Marker E steadylyellow incandescent Star Marker A pul sedlyel 1 ow incandescent Star Marker H steadylred incandescent Star Marker G pulsedlred Xenon DSL Marker D pulsedlred incandescent Star Marker B pulsedlred LED Pulse Marker C pul sedlyel 1 ow TCS

Worst visibility Marker F pul sedlred TCS.

Notice that the same markers suggested as "acceptable" from the rating data,

are also at the top of the rank order given above.

A rank order indicates the relative position of objects on some dimension (visibility in this case) but does not indicate how far apart the

ordered objects are from one another. In order to develop an interval scale

for the rank ordered markers which indicates how close (or far apart) on the

visibility continuum they are, additional assumptions are needed. A commonly used procedure for scaling pair comparison data is attributed to Thurstone

(1927) and was applied here. The background for this type of scaling will be

briefly described below to enhance understanding of results derived from it. The description of the method provided here borrows heavily from Dunn-Rankin

(1983). Thurstone postulated that for any stimulus, 1) people's reactions to

that stimulus are subjective, and 2) they vary randomly from moment to moment.

While reactions may vary, there is a most frequent reaction, called the modal

reaction. This mode can be estimated based on repeated judgments from a

single subject or, as in the present field test, the frequency of single

judgments from many subjects. Thurstone further assumed these reactions were

nornlal ly distributed. Because the mean and mode of a normal distribution are

the same, the mean can serve as a scale value for an object (such as a train

TABLE 6-2. PROPORTION MATRIX, P, SHOWING THE PROPORTION OF SUBJECTS WHO JUDGED THE MARKER AT THE TOP TO BE MORE V I S I B L E THAN THE EACH MARKER AT THE S I D E

MARKER A

A --- B .875 C .917 D .708 E .417 F .958 G .833 H .417

Note: EPj > P i *

Cells marked , n = 23 due to missing data ( n = no. subjects).

marker) on t h e psychological continuum o f i n t e r e s t , i n t h i s case, a v i s i b i l i t y

continuum.

I n t h e f i e l d study, subjects were asked t o judge which o f two

markers was more v i s i b l e f o r a l l p a i r s of markers. Using p a i r comparisons,

t h e propor t ions recorded i n Table 6-2 were co l lec ted. I f , as ind ica ted, 83 percent of subjects judged Marker H t o be more v i s i b l e than Marker B, then

according t o Thurstone, t h e average reac t ion t o Marker H should be h igher on a

v i s i b i l i t y sca le than t h e average reac t ion t o Marker B. Because o f t h e

normal i t y assumption mentioned above, p ropor t ions can be expressed as standard

normal deviates, e.g., i n t h e example, t h e normal deviate i s zBH = .97 ( f o r p

= .833), obtained from a standard normal table. This has been done i n Table

6-3. The scale separat ion between Marker H and Marker B on a v i s i b i l i t y

continuum can be made i n terms o f t h i s standard normal deviate, i .e., some-

where along t h i s continuum, Markers H and B are separated by a d is tance o f

-97, w i t h Marker H h igher on t h e v i s i b i l i t y scale.

The d i f fe rences between p a i r s o f markers can be obtained by use o f

t h e normal i t y assumption. I n p rac t i ce , t he average z-score f o r column markers

i s computed (see Gui l fo rd , 1954, pp. 161-163) and t h i s provides an i n t e r v a l

sca le o f v i s i b i l i t y (see bottom o f Table 6-3). Because i n t e r v a l scales have

a r b i t r a r y o r i g i n s (1 i ke t h e var ious temperature scales) , t h e z score averages

can be rescaled f o r convenience t o be greater than o r equal t o zero simply by

assigning t h e smal lest ( o r most negative) value t o be zero and s h i f t i n g a l l

o the r sca le values up accordingly. The r e s u l t i s g raph ica l l y presented i n

F igure 6-2. It can be seen t h a t Markers A, E, and H a re r e l a t i v e l y c lose

together i n terms o f v i s i b i l i t y . Markers D and G are c lose t o each o the r and

some d is tance below Markers A, El and H on the v i s i b i l i t y continuum. Marker B

i s r e l a t i v e l y c lose t o Marker D and G also. F i n a l l y , Markers F and C are

c lose together , somewhat removed from t h e o ther markers on t h e scale, and are

r e l a t i v e l y f a r down toward t h e negat ive end o f t h e continuum.

6.3 Detection Angles from Simulated Approach along an 11.5. Track

Visual performance data were co l l ec ted t o determine how e a s i l y

observers would detec t a marker dur ing a slow, curved t rack approach. I n

TABLE 6-3. THE STANDARD NORMAL DEVIATE MATRIX, Z, SHOWING THE PROPORTION OF SUBJECTS WHO JUDGED THE MARKER AT THE TOP TO BE MORE V I S I B L E THAN THE EACH MARKER AT THE S I D E

MARKER A

A 0.0 B 1.15 C 1.39 D .55 E -.21 F 1.72 G .97 H -.21

IZ 5.36 .96 -10.01 1.73 5.53 -10.16 2.00 4.60

Mean, .67 .12 -1.25 .22 .69 -1.27 .25 .58

- Marker H (I .85)

Visibility - Marker D (1.49), Marker G (1.52)

Scale - Marker B (1 39)

(Arbitrary 1 3

Zero Point l2

and Units) '.' 1 .o f

o t - Marker F (0), Marker C (-02)

'Numbers In parentheses are numerical scale values.

FIGURE 6-2. THURSTONE CLASS V INTERVAL SCALE OF REAR-END TRAIN MARKER V I S I B I L I T Y , 1000' TANGENT TRACK CONDITION

keeping w i t h t h e best caselworse case analys is , an 11.5" curve approach was

simulated (see Appendix A f o r f u r the r explanat ion) t o represent t h e most

extreme curve which would be encountered i n operat ion.

The median o f t h ree data t r i a l s f o r each subject f o r each marker

served as t h e data f o r ana lys is o f de tec t ion angles. The median was chosen as

t h e sumnary s t a t i s t i c f o r each sub jec t ' s data because, espec ia l l y f o r small

samples w i t h poss ib le o u t l i e r s * , t h e median provides a b e t t e r est imate o f t h e

popu la t ion mean than does t h e sample mean. However, s ince t h e populat ion

c h a r a c t e r i s t i c est imated i s mean detec t ion angle, i t i s s t i l l reasonable t o

t e s t hypotheses about means o f medians.

Table 6-4 presents t h e means, across subjects, o f t h e median detec-

t i o n angles f o r Markers A through H. A l l o f t he detec t ion angles reported i n

Table 4.4 are considerably greater than 57.3O. This imp l ies t h a t a l l markers

are acceptable because they a l l a f f o r d a t l e a s t 1000 ft o f stop-ping d is tance

on an 11.5O curved t r a c k (under t h e f i e l d t e s t condi t ions) . The S ta r markers

were detected most r e a d i l y i n p a r t because they had a lens design t h a t

protruded s u f f i c i e n t l y beyond t h e edge o f t he r e f l e c t o r housing so as t o a l l ow

de tec t i on a t angles s u b s t a n t i a l l y g reater than 90°. TCS markers a l so had

lenses t h a t protruded beyond t h e i r marker housing, though n o t as much as t h e

S ta r markers. The s i d e views o f t h e var ious markers used i n t h i s f i e l d t e s t

a re shown i n F igure 6-3. Even though a l l markers were equa l ly acceptable according t o t h e

1000 f t stopping d is tance c r i t e r i o n , t he re were s t a t i s t i c a l l y r e l i a b l e

d i f fe rences among them. These d i f fe rences are noted i n Appendix E. Cer ta in

observat ions regard ing marker c h a r a c t e r i s t i c s are appropr iate a t t h i s po in t .

Colors i n d i c a t e d by t h e l abe ls "red" and "yel low" do not r i g o r o u s l y de f ine

marker chromat ic i ty . (See Table 4-1, page 12, f o r spect ra l data on t h e

markers used i n t h e f i e l d t e s t ) . Rather, these labe ls simply stand f o r a

range o f sub jec t i ve impressions which most people would c a l l " red" o r

"yel low". S i m i l a r l y , c y c l e (i.e., pulsed o r steady) does no t capture such

design parameters as pu lse width, pulse per iod, shape o f t h e r i s e o r decay

funct ion, e t cetera. These t o o are l abe ls which capture t h e sub jec t i ve

* An o u t l i e r i s an extreme observation, we l l beyond a normal d i s t r i b u t i o n .

TABLE 6-4. MEAN PER WRKER, ACROSS SUBJECTS, OF MEDIAN DETECTION ANGLES, I N DEGREES

Mean ~n~ 1 ea ~ange' - -- Code Col o r Cycl e Lamp Type M f q .

A ye l l ow b l i n k Incandescent S ta r

B red b l i n k LED Pulse

C ye l low b l i n k Xenon pulse TCS

D red b l i n k Incandescent S tar

E ye l l ow n o b l i n k Incandescent S tar

F red b l i n k Xenon pulse TCS

G red b l i n k Xenon pu lse DSL

H red no b l i n k Incandescent S ta r

Notes: a - A l l angles are given i n degrees from the observer.

b - Numbers i n parentheses are standard deviat ions.

c - Ranges i n d i c a t e t h e minimum and maximum de tec t i on angles found du r ing t h e f i e l d t e s t .

A. S t a r Marker B. Transit Control Marker

C . DSL Marker D . Pulse Marker

FIGURE 6-3. S IDE VIEWS OF REAR-END MARKERS USED I N TESTS

impression of whether a given light source blinks or remains steady. With the understanding that they are qua1 itatively defined, tests of the effect of color and cycle on detection angles were conducted.

In order to assess the impact of color on mean detection angles, an analysis was conducted on blinking red and ye1 low Star and blinking red and

yellow TCS markers. This analysis seemed reasonable because the manufacturer of a marker was analyzed as a separate variable of two 1 eve1 s (Star and TCS) . This allowed for the separation of effects due to color and effects due to

factors other than color which were collectively referred to as differences

due to manufacturer. The factor of color was also of two levels (red, ye1 1 ow).

Table 6-5 presents the results of the field test in a contingency

table with levels of color as columns and levels of manufacturer as rows.

Means for red and yellow markers, averaged over both marker manufacturers,

were not statistically different. Means for Star and TCS markers, averaged

over red and yellow, were statistically different. There was also a signi-

ficant Color times Manufacturer interaction. These differences are noted in

Appendix E. There was a big difference. found between manufacturers. This main

effect is not surprising, given the results reported in Table 6-4. The

interaction suggests that the impact of color on detection angle depended on

the manufacturer of the marker. The yellow TCS marker was more readily

detected than the red TCS marker (means of 91.3" and 86.0°, respectively).

For the blinking Star markers, the reverse was true (means of 160.4" and

154.7", respectively, for bl inking red and ye1 1 ow markers). Another marker design variable of interest is cycle (blink vs. no

blink). Within the conditions of this field test, the Star lamps offered an

opportunity to test for the effects of cycle and investigate any interaction

which might exist between color (red, yellow) and cycle (blink, no blink).

(Star markers were used for this analysis because only Star markers came in both red and yellow, both blink and no blink). The results from the field

test are sumnarized in Table 6-6. Analysis of variance indicated no signifi-

TABLE 6-5. CONTINGENCY TABLE OF MEAN DETECTION ANGLES, COLOR (RED, YELLOW) BY MANUFACTURER (PULSED STAR, TCS)

Detection Anqle vs. Color Manufacturer Red Ye1 1 ow Row Means

Star

TCS

Column Means:

TABLE 6-6 CONTINGENCY TABLE OF MEAN DETECTION ANGLES BY COLOR (RED, YELLOW) AND CYCLE (PULSED, STEADY), STAR MARKERS

Detection Anqle vs. Color Light Cycle Red Ye1 1 ow Row Means

Steady

Pulsed

Column Means: 1 5 8 . 6 O 159.4"

cant main effect of color. Similarly, there was no main effect for cycle.

There was, however, a significant interaction between color and cycle. These effects are noted in Appendix E.

No other tests were conducted on this data because of confounding

factors which would have made interpretation impossible.

6.4 Discussion of Results

The results of the field test address both on-axis viewing of the

markers at 1000 ft (through subjective assessments of visibi 1 ity) and off-axis detection in a simulated approach along an 11.5O track (through visual perfor-

mance). It is important to keep in mind that the results reported above and

the discussion of those results given apply most directly to conditions like

those of the test. These conditions included excellent atmospheric transmis-

sibil ity (i .e., no rain, fog, snow) clean and properly functioning markers,

alert subjects undistracted by any other workload, a re1 atively uncluttered

test environment , and no vei 1 i ng reflections from a 1 ocomotive head1 amp.

These factors deserve analysis, but due to the complexity and considerable

time involved, an analysis of these factors was outside the scope of this

field test, Therefore, extrapolation from the current results (which might be

considered a baseline under near ideal conditions) must be made cautiously.

6.4.1 Subjective Ratinqs, Rankinqs and Scal in9 of Rear-End Train Marker Vi si bi 1 i ty

Consider first the results of the visibility ratings. In inter-

preting the confidence intervals given in Figure 6-1, recall that the con-

ditions of the field test were virtually ideal. Furthermore, consider also

that people were asked to use their own subjective (and presumably reasonable)

criterion of a marker's visibility, i .e., the ease with which the marker may

be seen. Given that actual operating conditions wi 1 1 not always be so ideal,

it seems prudent to be concerned about markers that would be judged less than

"Good" by most people. The cutoff defining "most people" is somewhat arbi-

trary, but it seems that, adopting the most lax criterion, the confidence

interval for the proportions of "Good" or "Very Good" ratings for a marker

should not extend below .50. (A t r u e propor t ion o f # = .5 i nd i ca tes t h a t h a l f t h e observers i n t h e populat ion would judge a marker's v i s i b i l i t y "Border l ine"

o r worse). Using t h i s c r i t e r i o n , t h e fo l l ow ing markers seem t o o f f e r adequate

v i s i b i l i t y : Marker A, D, E, G I and H, i.e., a l l S ta r markers and t h e DSL

marker. The c u t o f f can be varied, o f course, t o more s t r i n g e n t o r more l e n i e n t leve ls .

A c r i t i c i s m o f t h e above arguments may be tha t , i n f a c t , a l l subjects i n t h e f i e l d t e s t saw a l l markers a t 1000 ft, thereby meeting t h e

FRA's suggested stopping d is tance c r i t e r i o n . However, t h e f a c t t h a t t h e f i e 1 d t e s t was conducted under near i d e a l cond i t ions suggests caut ion about markers

judged by a subs tan t ia l p ropor t ion o f people t o be less than good. The 95 percent Confidence I n t e r v a l w i t h 0.5 c u t o f f c r i t e r i a i s one attempt t o

q u a n t i t a t i v e l y de f ine t h i s concern i n terms o f a decis ion r u l e .

Consider next t h e rankings and sca l ing resu l t s . The ra t i ngs , taken

w i t h reference t o each sub jec t ' s own standard o f " t h e ease w i t h which a marker

may be seen", d i d provide some i n d i c a t i o n o f t he a c c e p t a b i l i t y o f var ious

markers w i t h respect t o v i s i b i l i t y under the cond i t ions o f t h e f i e l d t e s t .

However, t h e r a t i n g data d i d no t r e a l l y provide a comparison among markers.

Ranking does, b u t i t on ly shows the r e l a t i v e p o s i t i o n on an ordered l i s t o f

t h e rear-end t r a i n markers. It provides no in format ion on how d i f f e r e n t t h e

markers might be from one another o r whether s p e c i f i c markers are above o r

below an a c c e p t a b i l i t y th resho ld f o r v i s i b i 1 i t y . Scal ing provides add i t i ona l

in format ion about t h e r e l a t i v e d is tance between markers on t h e v i s i b i 1 i t y

continuum, b u t a l s o does n o t i n d i c a t e t h e a c c e p t a b i l i t y o f marker 's

v i s i b i l i t y .

Thus, ra t i ngs , rank i ngs, and scal i n g analyses complement one another

i n he lp ing t o understand t h e perceived v i s i b i l i t y o f rear-end t r a i n markers

under t h e cond i t i ons o f t h e f i e l d t e s t reported here. Taken together , t h e

conclus ion i s t h a t , based on t h e sub jec t i ve assessment data c o l l e c t e d under

t h e cond i t ions o f t h e f i e l d t e s t , Markers A, D, E l G I ( the S ta r markers) and H

( the DSL marker) should be q u i t e v i s i b l e under operat ional cond i t ions s imi 1 a r

t o those of t h e f i e l d t e s t . On t h e o ther hand, even though a1 1 markers were

v i s i b l e t o a l l subjects, ra t i ngs , rankings, and scale values suggest t h a t t h e

v i s i b i l i t y o f Marker B ( the Pulse marker) i s r e l a t i v e l y border1 ine, and

markers C and F (TCS markers) under l ess than idea l cond i t ions are suspect.

A l l o f these conclusions are intended to, apply on ly t o slow approaches on a

tangent ( s t r a i g h t ) t r a c k w i t h detec t ion a t 1000 ft; as an observer approaches

c lose r and c lose r t o a marker, i t s v i s i b i l i t y w i l l presumably increase.

6.4.2 Discussion o f Detect ion Anqle Results from Simulated Approach Along an 11 -5: Curved Track

The most important r e s u l t o f t h e detec t ion angle data i s t h a t a l l

de tec t ion angles were greater than t h e 5 7 . 3 O needed t o a f f o r d a t l e a s t 1000 f t

o f t rack stopping d is tance dur ing a slow approach along such a curved t rack .

This imp1 i e s t h a t a l l markers tes ted were acceptable w i t h respect t o t h i s

c r i t e r i o n .

Simple t e s t s o f marker manufacturer (Star and TCS) and marker c o l o r

(red, yel low) were made t o assess t h e impact c o l o r had on o f f - a x i s detect ions.

Results (see Table 6-4) i nd i ca ted tha t , as expected, manufacturer d i f f e rences

were . s i g n i f i c a n t ( i .e., S ta r markers were detected more read i l y than TCS

markers). However, t h e r e was a manufacturer times c o l o r i n t e r a c t i o n such t h a t

b l i n k i n g ye l l ow TCS markers were detected more r e a d i l y than b l i n k i n g red TCS

markers; t h e reverse was t r u e f o r S tar devices. A p laus ib le (though incom-

p l e t e ) explanat ion f o r t h i s i n t e r a c t i o n i s o f fe red i n terms o f t h e design

d i f fe rences between S t a r and TCS markers.

Consider f i r s t t h e physical design o f t h e markers (see Figure 6-3).

The housing o f a TCS marker exposed less o f t he lens t o an observer than t h e

design o f t h e S ta r markers a t any given viewing angle o f 90" o r greater . This

must have con t r i bu ted t o l a t e r de tec t ion t ime w i t h t h e TCS markers. A design

i m p l i c a t i o n i s t h a t t h e lore a marker lens protrudes beyond t h e r e f l e c t o r

housing, t h e more r e a d i l y i t may be detected dur ing approaches on curved

t rack. A second f a c t o r c o n t r i b u t i n g t o the i n t e r a c t i o n between manufacturer

and c o l o r may be due t o d i f fe rences i n br ightness. Subject ive impressions

were t h a t t h e TCS markers were dimmer than t h e S ta r markers and t h i s may be

explained by Bloch's law (Shiffman, 1976). Bloch's Law says t h a t , f o r dura-

t i o n s of about 100 mi l l i seconds o r less, t he product o f s t imulus i n t e n s i t y (I)

and st imulus du ra t i on (t) equals a constant (K) which i s r e l a t e d t o perceived

brightness, i .e., I x T = K. Beyond 100 msec, perceived brightness i s a

func t ion o f st imulus i n t e n s i t y alone. I n the present case, the pulse width o f t he TCS markers was considerably shorter (around 25 nanoseconds) than t ha t f o r the Star markers (around 250 mil l iseconds) over roughly the same pulse per iod

(1 second f o r each make). The reciprocal re la t ionsh ip between i n t e n s i t y and

b l i n k durat ion given i n Bloch's Law impl ies t ha t the greater peak i n tens i t y o f

TCS xenon lamps was undermined by a pulse width which was too short. This lowered the apparent brightness o f the TCS lamps t o a leve l where the higher

luminance o f TCS ye l low over TCS red was s i g n i f i c a n t l y advantageous t o o f f -

ax is detect ion. The design imp l i ca t ion o f t h i s i s t h a t pulse periods and peak

i n t e n s i t i e s must both be defined i n r e l a t i o n t o one another t o support a spec i f i ed l e v e l o f v i sua l performance.

The explanation o f why b l i nk i ng red Star markers were detected more

r e a d i l y than b l i nk i ng yel low Star markers i s unknown a t t h i s time. A check of

the data ind icated the super io r i t y o f b l i nk i ng red markers was qu i t e pro-

nounced: twenty-two (22) out o f twenty-four subjects detected i t more readi l y

than the b l i n k i n g yel low marker.

Another t e s t was conducted t o compare the impact o f cyc le (b l ink , no

b l i n k ) and co lo r (red, yel low) on of f -axis detect ion performance ( f o r the Star

markers only). As ind icated i n Table 6-6, b l i nk i ng red Star markers were

detected more read i l y than steady red Star markers, but the opposite e f f e c t

was observed f o r the ye l low markers: steady yel low Star markers were detected

more read i l y than b l i n k i n g ye l low Star markers. B l ink i s commonly used t o

enhance the d e t e c t i b i l i t y o f a l i g h t source, espec ia l ly when t ha t source i s

r e l a t i v e l y dim, t o be viewed a t n ight , o r l i k e l y t o be viewed w i th per ipheral

v is ion. I n the present case, the red Star markers were dimmer than the yel low

markers (see Ross and Grieser, 1988). One possible explanation i s t ha t they

were o f such a luminance t h a t the added v isual 'motion' o f b l i n k s i g n i f i c a n t l y

helped make the b l i n k i n g red markers more de tec t i b l e than steady red markers.

What i s there, then, t o explain the opposite pat tern o f r esu l t s

w i t h the ye l low Star markers which were r e l a t i v e l y b r i gh te r than the red ones?

One t en ta t i ve explanation i s t h a t b l i n k may have simply reduced the overa l l

apparent brightness o f the b l i nk i ng yel low marker when compared t o a steady

ye l low marker. There i s evidence (e.g., Talbot 's Law) t ha t the v isua l system

averages the amount o f t o t a l luminance received during l i g h t and dark phases

o f a b l i n k cyc le (Shiffman, 1976). A steady l i g h t would therefore be

perceived as b r i gh te r than a b l i nk i ng one, under the proper conditions. The Thurstone scal i ng data a lso showed t ha t steady 1 igh ts were o f cons is tent ly

(though s l i g h t l y ) be t t e r v i s i b i l i t y . The Star co lo r x b l i nk in te rac t ion ,

then, suggests a compromise on design. I f actual t r a i n operations w i l l

i nvo lve an observer f i r s t detect ing a rear-end t r a i n marker w i t h per ipheral

v is ion, i t may be most e f f e c t i v e t o use a ye1 low marker such as the Star ( f o r

greater brightness than the corresponding red Star marker provides) but

inc lude b l i n k ( t o provide v isua l motion).

As was mentioned previously, no other tes ts were conducted on t h i s

data because o f confounding fac tors which would have made in te rp re ta t ion

impossible. A l l explanations o f fered above must be considered hypothetical

only. A1 t e rna t i ve explanations may a1 so be avai 1 able.

6.4.3. The E f fec ts o f Glare from Rear-End Tra in Markers

One f ac to r o f i n t e res t i n evaluating rear-end t r a i n markers i s the

g l a re t h a t they may cause. D i rec t g lare from markers can be discomforting,

impai r v isua l performance, o r both. Unfortunately, an assessment o f the g l are

proper t ies o f the markers used i n the f i e l d t e s t was beyond the scope o f t h i s

study. This i s because the e f fec ts o f a d i r ec t g lare source are a complex

funct ion o f several variables. A primary var iable i s distance t o the source.

Almost any b r i g h t 1 i g h t source can become g la r ing as one approaches it, not

because i t i s ge t t i ng b r i gh te r but because i t i s v i sua l l y looming t o assume a

l a rge r and la rger proport ion o f the v isual f i e l d . Another primary var iab le i s

the v e r t i c a l d i f fe rence between the marker and the observer's l i n e o f sight;

the marker, located a t coupler height, i s much lower than the locomotive

engineer seated i n the cab. As the observer approaches i n a locomotive,

however, the marker begins t o drop below the observer's 1 i ne o f s i gh t such

t h a t when a locomotive i s located imnediately behind the t r a i n , the marker

w i l l be we l l below the observer's l i n e o f s ight . When one considers f u r t he r

t h a t g l a re i s a funct ion o f the v isua l system's s ta te o f l i gh t / da rk adapt-

a t ion, presence o f other l i g h t sources i n the background, and involves both

discomfort and disability, an analysis of glare properties is a study unto

itself. It is for this reason that no glare assessment data are included in

this report. Such a study might plot discomfort glare (which is subjectively

determined) as a function of distance to the marker. It might also assess any

disability caused by means o f a visual test.

7.0 S W R Y AND CONCLUSIONS

7.1 Laboratory Tests

Laboratory tests were conducted on the train rear-end marker devices

from four manufacturers. Chromaticity (color) measurements were made for each device to determine irradiance versus wavelength over a range from 380 to 780

millimicrons. Peak intensity measurements were made using a telephotometer at distances of 25 and 100 ft, both on the geometric center and *90° from this

center on the horizontal and vertical axes. For the pulsed lamps, effective intensities were calculated from peak intensities and integrating the pulse

shape versus time, and using the appropriate formula from the IES Lightinq

Handbook.

Results from these tests showed that all units met the FRA color

range requirements. For the slower pulsed units (Pulse, Star -- typically a 114 second pulse duration), peak intensities on-axi s exceeded the FRA minimum

of 100 candela. Off-axis (*15O horizontally, *5O vertical ly) , the Pulse devices fell near or below the FRA minimum of 50 candela; while the Star

devices (particularly with the amber lens) exceeded the minimum. Effective

intensity for these units (in candela-seconds), based on the IES formula, fell

below the given minima, except for the Star units with amber lense.

For the xenon flash tube devices (DSL, TCS -- typically a 20 micro- second pulse duration), peak intensities exceeded the FRA maximum of 1000

candela. Effective intensities for the DSL units exceeded the FRA minimum of

100 on axis, but fell below the FRA minimum of 50 off axis. Effective inten-

sities for the TCS units fell below 1.0, a factor greater than 100 below the

FRA minimum.

Comparison of these test results with tests conducted by ETL Testing

Laboratories, Inc., on the same or similar devices showed that Battelle's peak

intensity measurements were substantially lower than ETL's. Direct comparison

of measurements with both sets of equipment on three of the devices, using the

same set-up procedures, showed good correlation between results. Based on

this comparison, we conclude that the major differences in intensity values

are the r e s u l t o f device mounting. Where B a t t e l l e chose t h e geometric center

f o r i t s measurements, ETL.chose the lamp "hot spot" (po in t of maximum in ten -

s i t y ) f o r i t s readings. I n f u t u r e t e s t i n g , t he device mounting pro toco l must

be taken i n t o cons idera t ion so t h a t consistency i n r e s u l t s may be achieved.

7.2 F ie l d Tests

A f i e l d t e s t was conducted t o assess t h e v i s i b i l i t y t o human

observers o f a sample o f rear-end t r a i n marker d i f f e r i n g i n lamp type, co lo r ,

cyc le (pulsed o r steady) and luminance. Both sub jec t i ve assessments and

v i sua l de tec t i on da ta were co l lec ted . The f o l l o w i n g i s a summary o f r e s u l t s

and conclusions w i t h respect t o v i s i b i l i t y o f t h e markers tested:

1. A l l markers used i n t h i s f i e l d t e s t a f fo rded adequate o f f - a x i s de tec t ion , under the cond i t ions o f t he t e s t , us ing t h e 1000 f t t r a c k stopping d is tance c r i t e r i o n ;

2. A l l markers used i n t h i s f i e l d t e s t were v i s i b l e t o a l l sub- j e c t s i n a 1000 f t on-axis viewing cond i t i on which simmulated an approach on tangent t rack;

3 . Despite t h e e q u a l i t y o f markers w i t h reference t o an accept- ablelunacceptable th resho ld f o r a f f o r d i n g a t l e a s t 1000 f t o f t r a c k stopping d is tance upon detec t ion dur ing a 15-mph slow approach, f i e l d t e s t data d i d d i s t i n g u i s h among markers.

4. I f markers are ranked i n order o f o f f - a x i s d e t e c t i b i l i t y based on mean de tec t i on angles, t he f o l l o w i n g l i s t emerges, i n terms o f f i r s t detected:

Marker E Star , Ye1 lowlsteady (incandescent) -- 164O Marker D Star , Redlpulsed

Marker t incandescent) -- 160°

Marker H Star , Redlsteady incandescent) -- 157" A Star , Ye1 low/pul sed (incandescent) --

-- 155O

Marker C TCS, Ye1 low/pul sed (Xenon f 1 ash) 91° Marker F, TCS, Redlpulsed (Xenon f l ash ) -- 86" Marker G I DSL, Redlpulsed (Xenon f l ash ) -- 85" Marker B, Pulse, Redlpulsed (LED) -- 84"

5. Using t h e o f f - a x i s de tec t i on t e s t cond i t ions , S ta r markers were f a r more r e a d i l y detected than any o f t he o the r makes. When co r rec ted f o r t he f a c t t h a t 90° i s t he l a r g e s t viewing angle o f p r a c t i c a l i n t e r e s t , t h e S ta r markers are s t i 11 t h e best, bu t t h e i r s u p e r i o r i t y i s reduced s u b s t a n t i a l l y .

6. Color e f f e c t s on o f f - a x i s de tec t ion were no t simple. Given b l i n k i n g markers such as the TCS Xenon devices, ye1 low seems t o o f f e r an advantage over red. For markers such as t h e b l i nk ing S ta r devices, red seems t o o f f e r an advantage over ye1 low.

7. S i m i l a r l y , c o l o r and cyc le (pulsed o r steady) do no t have simple e f f e c t s w i t h markers such as t h e S ta r lamps. Under t h e o f f - a x i s de tec t ion cond i t ions o f t he t e s t , b l i n k i n g red markers were detected e a r l i e r than steady red markers. However, steady ye1 low markers were detected more readi l y than b l i n k i n g ye1 low markers.

8. Sub jec t ive evaluat ions o f v i s i b i l i t y ( ra t ings , rankings, and scal i n g o f t h e markers) d i f f e r e n t i a t e d among t h e markers: S ta r and DSL markers were judged most v i s i b l e o f t he l o t tested.

9. The marker ind ica ted by the f i e l d t e s t data as being most r e a d i l y d e t e c t i b l e i n both s t r a i g h t and curved approach cond i t ions i s t h e Star, ye1 lowlsteady incandescent marker.

10. I f actual t r a i n operat ions w i l l i nvo l ve an observer f i r s t de tec t i ng a rear-end t r a i n marker w i t h per iphera l v i s ion , i t may be most e f f e c t i v e t o use a ye l l ow marker such as t h e S ta r ( f o r g reater br ightness than Star red provides) , bu t inc lude b l i n k t o provide a t ten t ion-catch ing v i sua l motion f o r an observer who may be d i s t r a c t e d by o ther dut ies.

This f i e l d t e s t was conducted under near i d e a l environmental and observer condi t ions. It i s most p roper ly considered a base1 i n e comparison o f a sample o f rear-end t r a i n markers. Ef fect iveness o f t h e markers under vary ing cond i t ions o f atmospheric transmi s s i b i 1 i t y (fog, r a i n , snow) , d i r t bui ldup on t h e lens o f t h e markers, obscurants on t h e cab windshield, c l u t t e r i n the v i sua l f i e l d , h igh workload on t h e observer, etc. were n o t evaluated. These were considered t o be outs ide t h e t ime and budget resources o f t h i s cont rac t .

Under t h e cond i t ions o f t h e t e s t , a l l markers are acceptable from t h e standpoint o f t h e v i sua l performance c r i t e r i a mentioned above. This suggests other, non-visual, c r i t e r i a be used f o r d i s t i ngu ish ing among markers, i f necessary. These c r i t e r i a might inc lude cost , r e l i a b i l i t y , a v a i l a b i l i t y , and mainta inabi 1 i ty. A l te rna t i ve l y , t h e r e s u l t s suggest t h a t several d i f f e r e n t designs o f rear-end t r a i n markers w i l l be acceptable from a human fac to rs standpoint.

7.3 Recotmendat ions for Future Research

The following recomnendations for future research are offered to the

Federal Rai 1 road Administration (FRA) for their consideration. It is be1 ieved

that projects such as those listed below will contribute to a better under-

standing of active rear-end train marker technology from the standpoint of

human observers. The following studies are recommended:

1. An archival study to compile existing guidelines on the design of rear-end train markers (and similar devices). Such a study would review existing literature to collect useful guidance on design parameters which yield superior markers and signage. Sources would include 1 iterature in visual science, psychology, human factors, special studies conducted in the transportation arena (rai 1, air, sea, and road), DOD standards and guide1 ines, foreign standards and guidelines, etc. This resulting guide- lines manual could support revisions of the Code of Federal Regulations, Part 221 as well as suggest gaps in understanding of marker design. It is anticipated that such a manual would be useful in other areas of DOT as well.

2. A study of the nature of glare associated with active rear-end train markers similar to the one briefly described in Section 6.4. An enhanced understanding of glare effects associated with rear-end train marker devices would provide data to guide the design or selection of markers which are acceptable to railroad engineers and enhance railroad safety.

3 . An assessment of factors which may constrain the applicability of the results reported in this field test. Such factors as observer workload, obscurants, headlamp effects, visual clutter, and locomotive engineer preferences might be addressed in such research.

REFERENCES

Cornsweet, T. N. (1970). Visual percept ion. New York: Academic Press.

Devore, J. L. (1982). P r o b a b i l i t y and s t a t i s t i c s f o r engineerinq and the sciences. Monterey, CA: Brooks/Cole Pub1 i s h i ng Co.

Dunn-Rankin, P. (1983). Scal ing methods. H i 11 sdale, NJ: Lawrence E r l baum Associates.

Gui 1 fo rd , J. P. (1954). Psychometric methods. New York: McGraw-Hi 11 . Riggs, L. (1971). Vision. I n J. K l i n g & L. Riggs (Eds.), Woodworth and Schlosberq's experimental psychology (Th i rd ed i t i on ) . New York: Hol t, Rinehart, and Winston.

Ross, D: , & --- Grieser, D. (1988, December). Rear-end t r a i n marker 1 i g h t eva luat ion Laboratory t e s t r e s u l t s (Contract No. DTRF53-86-C-00006, Task 7). Columbus, OH: B a t t e l l e Columbus Div is ion .

Sherman, R., Ray, H., & Meacham, H. (1984, Ju l y ) . Rear-end Marker Study (FRAIORD-84/14). Columbus, OH: Ba t te l l e Columbus Laborator ies.

Shiffman, H. (1976). Sensation and perception: An in teq ra ted approach. New York: John Wiley.

Thurstone, L. (1927). A law o f comparative judgement. Psychological Review, 34, 273-286.

APPENDIX A

SPECTRAL DATA

- DSL HVM-301-00F -

#2957 - : - j

i I'll ,' :/ '!, - I

I I

- J

i - i

I

-- j I I I I I I ' I I I I I I I I

390 1

4sl0 I

510 I

5!0 I I I I

630 I 690 740 nanone t e r s

;'-; <. - ( "-4 '.,.,, .' ,. .. 1 . - i .-.' , 8'.

I '., . " . j '\.,. ;, /I - I 1, .'be

#2981 i la/ 'I

- / 'I 1 \

i i i; \ - i

I - I . . i

I \----.-!

- I I - I I

-

- ;.

I I I I I I : I 1 I I I I I I I I I I I

I

390 4$ 0 5i0 5 \ 0 630 690 7$0 nanone t e r s

FIGURE A-1. SPECTRAL RESPONSE OF DSL REAR-END MARKER DEVICES

a-1

nanone t e r s

FIGURE A-1 . (continued)

nanone ters

108 - N 90 0 r 80 n

70

I 60

P r 50

8 40 1 a 30 n c 20 e

10

0

FIGURE A-2. SPECTRAL RESPONSE OF PULSE REAR-END MARKER DEVICES

.-

.- PULSE TRAINLINK #203

-- .- .- I /\ .- /' \ .-

.- i i

\ \ .- 1 \,

'r., \

I I I I I I I ---*' I I 1..

- I I I I 1 I I I- I

398 4i0 510 5'r 0 638 6911 758 nanone ters

...-' I I I I I - I I I I

I I I I

I

394 I 4ie tiin 5'le 630 I I 1

690 7$0 nanone ters

FIGURE A-3. SPECTRAL RESPONSE OF STAR MARKER DEVICES, RED LENSE

a-5

100 -

N 90 0 r 80 n , 70

I 60 r r 50

40 i a 30 n c 20 e

10

0

..-' .---

-- --

#R2 .- J

.- i

.- / ,/'

.- ./'

.- ---- ,'- i

.- ,.fi

.- i' :

-- i i

- I -.*..

I I I I I I I I I I I I I I I I

390 I 4 i0 510 5'lO 638 690 740 nanone ters

100 -

N 90 o r 80 n , 70

I 60 P r 50

48 1 a 38 n c 20 e

10

8

STAR 845F R E D IRZ. STEADY S I A I E LOWRITHnlC

/.-- >,

/..- .-

STAR 845F RED #R2 .- STEADY -- .-

.-

.- -1'.

,.a. /..- .-

--

i. .-

. ; I I I I

I

1E-1

5E-2

1E-2 . I 5E-3 . r P a 1E-3 . d 5E-4 . i a n 11- 4 . c 5E-5 e

1E-5 5E-6 .

1E-6 -

FIGURE A-3. (continued)

390 I 4sfe sin 5'/0 630 694 7S0

I , i '! i I

nanone ters

390 4 i0 sf 0 s'le 630 I 690 748 nanone t e r s

, ------- --- -----

/'-

i i

I

..;'a-

/ ./ --. -. I

I

.- /--) -. : J '\,{ -

/. I

I I

I

I I \ ' I b.l

I I I , I I I I I I I I I I

I I I I

/ 0 1 ; I I I I i l I I I I I I I I

.... I I

I

390 I 4 h 510 5'l0 630 I 690 I I

7$0 nanone t e r s

FIGURE A-4. SPECTRAL RESPONSE OF STAR MARKER DEVICES, AMBER LENSE

a-7

100

N 90 0 r 80 n

70

I 60 r r 50

! 40 i a 30 n c 20 e

10

0

* ,...- ...' 4-

.---- .,'-

.- # Y 2 /

.- a-

/'

.- ,.---- i

/" ,- /

i .- -...---->* -2'

.- ,,---

.- / ../

- r I 1 I I I I I I I I I I

I I I I I

390 ~rie 510 5'le I 630 690 7$0 I

nanone ters

lE-5 J I ,i.J

I I I I I I I I I I I I

390 4< 0 I sic I

5'le I I I I

630 690 7$0 nanone t e r s

100

I 90 I

80 I , 70

[ 60 ? ? 50

40 I I 30 1 : 28 ?

10

0

STAR 845F MWBER 112, STEADY S T A I E L W R I T W l l C

- - ,.-- -- ,..- -- i'

-- STAR 845F AMBER #Y2 STEADY

.-

.-

.- .--- /' / / -- .*A- /

.- -.&/

.- /'

.- /

I I I I -.; /'

< : I I I I I I I I I I 1 I I

FIGURE A-4. (continued)

a-8

3911 I 4ie sia 5i0 638 6911 750 n a n o ~ e ters

I I I I I I ! I I I I I I I 1 I I 1

390 4i0 510 5!0 630 690 7Se nanone t e r s

- - - #I03

;-..pa - , 'e,

I ? I - ;\ l ',., 8. .:, ," -;' 8, I

- i 'I' ?-..'

8 , - 0 I

I ! : I . # I - I I

: i' - i

1 1 -

i - !'

I I I I I

1 I I I I I I I I 1 I I

1

390 450 510 ' 5tfl 630 690 ' 7$0 nanone t e r s

FIGURE A-5. SPECTRAL RESPONSE OF TCS REAR-END MARKER DEVICES

48 .-

30 .- I

20 .-

18 .-

8 . f

i I iI

I I I I I I I I I I I I I I I

390 4i4 510 5!0 638 698 750 nanometers

I I I I I I I I I I I I I

I I I

390 I 4$0 510 570 I 6i0 690 7$0 nanone t e r s

ICS 5390 I104 LOGARITHMIC

FIGURE A-5. (continued)

APPENDIX B

ANGULAR INTENSITY DATA AT 25 FEET

Horizontal Intensity at 25 ft. ICN the DSL 6ghl2957.

. . - . . - - - . . . - - - -

/

-. . . .- -

-70 - 5 0 -30 -10 D 30 50 7 0 90

mgle.lrom obrerverr view.nagalive kll peak horizontal

Vertical Intensity at 25 f t .

angle ltom obaerverm view.nega1ive down peak varlical

FIGURE B-1. ANGULAR INTENSITY AT 25 FEET, DSL 12957

b-1

Horizontal Intensity at 25 ft. lor Ihe OSL Gghl2981.

angle lrom obaerverm view.negalive Is11 peak horizonlal

Vertical Intensity at 25 ft. lor Ihs OSL bghl 2981.

angls.lrom obacrver8 view.negaIlve down peak v a r l ~ o l

F IGURE B-2. ANGULAR INTENSITY AT 25 FEET, DSL P2981

b-2

ngk. lrom obaarvaa vnw.negaliv4 loll paak hotkonlrl

angle.from obaarvera view.ncgalive down roak varl'idl

FIGURE B-4. ANGULAR INTENSITY AT 25 FEET, PULSE #203

b-4

Vertical Intensity at 25 ft. loc Iha PULSE Sghl204.

angls.lrom obasrvcrm viow.negalive down paak ve~lical

FIGURE B-5. ANGULAR INTENSITY AT 25 FEET, PULSE 5204

b-5

a n g l e . l r a obmorvn8 view.nogalivo loll peak hortzontal

anglo.lrom obmorvors vnwnegalive down oodk vertical

FIGURE B-6. ANGULAR INTENSITY AT 25 FEET, PULSE #205

b-6

Horizintal Intensity Dist. at 25 ft.

ngla.lrom obaervna &w.negaVwe kll I 1 peak horizontal

Vertical Intensity Dist. at 25 ft. lo# (he STAR rad tighl.RL

.ng*.lram obmvmra viawnegativa down L1 poah vertical

FIGURE B-7. ANGULAR INTENSITY AT 25 FEET, STAR RED LIGHT R1

b-7

Horizintal Intensity Dist. at 25 11. for Ih. STAR red EghlR2

-90 -70 -50 -30 -10 U) 30 50 70 90

angk.lrom obmervna v iowmgalwe k l t rl peak horizonla1

Vertical Intensity Dist. at 25 ft. lor the STAR rod EghlR2

angla.from obaerverm visw.nogalive down r l peak varlical -

FIGURE B-8. ANGULAR INTENSITY AT 25 FEET, STAR RED LIGHT R2

b -8

Horizontal Intensity Dist. at 25 11.

mgla.lrom obaorvma viaw.nagalive loll I I peak horizmld

Vertical Intensity Dist. at 25 ft. lor Ihe STAR amber Cghl.YL

angle.from ob~mverm view.nsgatiwa down I I peak verl~cal

FIGURE B-9. ANGULAR INTENSITY AT 25 FEET, STAR AMBER L I G H T Y 1

b-9

Horizontal Intensity Dist. at 25 11. lcw Ih. STAR d r Gghl.Y2

-90 -70 -50 -30 -10 K) 30 50 70 90

.mlle.lrom obwrvars &w.negalive kll I I paak horizontal

Vertical Intensity Dist. at 25 11. lor Iha STAR arnbn Egh1.12

450

mglo.from obsarvars viaw.nagalive down I I peak verlical

FIGURE 6-10. ANGULAR INTENSITY AT 25 FEET; STAR AMBER LIGHT Y2

b-10

Horizontal Intensity at 25 ft. lor Ihe TCS Fqhl D2.

. . - - -- ...

- - -- --

--

0.7 -. -- - -

0.5 ...... . . --

0.3 ... ..... . . ........

-90 -70 -50 -30 -10 10 30 50 70 90

angle.lrm observers view.negalivs lell peak hwizonI.4

Vertical Intensity at 25 ft. la Iho TCS Tqhl 102.

angk.from observers view.negalive down peak verlical

FIGURE B-11. ANGULAR I N T E N S I T Y AT 25 FEET, TCS t102

b-11

angle . f ra obaervar, viaw.nagaliva tall peak hnizonlal

Vertical Intensity at 25 ft.

angte.from observers viow.negative down peak vertical

FIGURE B-12. ANGULAR INTENSITY AT 25 FEET, TCS 5103

b-12

Horizontal Intensity at 25-11. tor the TCS light 104.

-90 -70 -50 -30 -10 10 30 50 7 0 90

angle.from ohnervere viswmgalive tell peak horizontal

Vertical Intensity a t 25 11. tor Ib TCS baht 104.

. ngle.lrom ob.wverm view.negalive down -. -- peak vertical

FIGURE B-13. ANGULAR INTENSITY AT 25 FEET, TCS 5104

b-13

APPENDIX C

ANGULAR INTENSITY DATA AT 100 FEET

Horizontal Intensity at 100 ft. la Ih. DSL Cgh1.2957.

Vertical Intensity at 100 11. la Ihe DSL Egh1.2957.

angle.lrom obmwvarn vnw,nogaliva down -- peak vsrliial

FIGURE C-1. ANGULAR INTENSITY AT 25 FEET, DSL #2957

c-1

Horizontal Intensity at 100 ft.

m g l e . f r m ob8ener8 view.negalive left - peak horizmlal

Vertical Intensity at 100 11.

angle.lrom obmmvafa vww.nogaliva down .- peak varlieal

FIGURE C-2. ANGULAR INTENSITY AT 100 FEET, DSL f2981

c-2

Horizontal Intensity at 100 ft. lor Ihe OSL lighl.2992.

angls.lrom obsefvers viaw.nsgaliva lell -- peak horizonlal

Vertical Intensity at 100 11. for Iha OSL ligh1.2992.

angle.lrom observars view.negalive down peak vor l ia l

FIGURE C-3. ANGULAR INTENSITY AT 100 FEET, DSL 52992

c-3

.ngh.lran ob@ervna view.nsgalive loll peak hmizomldt

Vertical Intensity at 100 f t . IOT Iha PUSE Ighl. 203.

angle.lrom obmervers view.negaliva down w a k vsrlical

FIGURE C-4. ANGULAR INTENSITY AT 100 FEET, PULSE #203

a n g k . l r a obaarvna viaw.negaliva lsll peak hor i rmt~ l

Vertical Intensity at 100 11. Iu Iha P U S € Eghl. 204.

mgk.lrom obsarvsrm v~ewnegaliva down peak vaflical

FIGURE C-5. ANGULAR INTENSITY AT 100 FEET, PULSE #204

Horizontal Intensity at 100 ft.

Vertical Intensity at 100 ft.

angle.lrom oba.rv.rm vkw.negalive down p.ak verlical

FIGURE C-6. ANGULAR INTENSITY AT 100 FEET, PULSE f205

angla.lran obaervam v k w . ~ g a l i i e *It I I peak horizontal

Verlical lnlensity at 100 ft. la Iha STAR Sghl. rl.

-96 -70 -50 -30 -10 16 30 50 70 90

mg(a.lrom obaerv.ra view.negativm d a m I I peak vertical

FIGURE C-7. ANGULAR INTENSITY AT 100 FEET, STAR RED LIGHT R1

c-7

Horizontal Intensity at 100 11. lor Ih. STAR red iigh112

-90 -70 -50 -30 -10 10 30 50 70 90

Vertical Intensity at 100 11. la th. STAR ighl. 12

-6 -70 -50 -30 -M D 30 50 70 9 0

anglo.lrom obmavsra view.negalivs down I I peak varlical

FIGURE C-8. ANGULAR INTENSITY AT 100 FEET, STAR RED LIGHT R2

C-8

Horizontal Intensity at 100 ft.

dngk.lrom obasrvws viow.negaliva left I I ~ a a k horizontal

Vertical Intensity a t 100 ft.

angle.lrom obssrvars view.nsgaliva down I I peak vertical

FIGURE C-9. ANGULAR INTENSITY AT 100 FEET, STAR AMBER LIGHT Y1

c-9

Horizontal Intensity a t 100 ft. lor Iha STAR y e b w 6ghl.yZ

2 0 -

-90 -70 -50 -30 -10 K) 30 50 70 90

Vertical Intensity at 100 11.

nq*.lrom obaavera viaw.negaliw. down I I wak varlical

FIGURE C-10. ANGULAR INTENSITY AT 100 FEET, STAR AMBER LIGHT Y2

c-10

Horizontal Intensity at 100 ft. lor Ih. TCS Ighl.lO2.

2.1 2

1.9 1.8 1.7 1.6 L5 1.4 1.3 12 II I

0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

-90 -70 -50 -30 -10 10 30 50 70 90

ang1e.from obaervera viewngalwe hfl -- peak horizontal

Vertical Intensity at 100 11. lor Ih. TCS Cgh1.102

-90 -70 -50 -30 -10 Y) 30 50 70 90

angla.lra obnnvera viewn.galive down --- peak varlkal

FIGURE C-11. ANGULAR INTENSITY AT 100 FEET, TCS #I02

c-11

Horizontal Intensity at 100 ft. la lhe TCS kgh1.103.

ang*.lrrm obaervaa vkwmgalivo kll - peak horirmld

Vertical Intensity at 100 11. la lho TCS Sgh1.103.

mgk.from obaavmm view.nogalivo down -. . peak verlical

FIGURE C-12. ANGULAR INTENSITY AT 100 FEET, TCS f 1 0 3

Horizontal Intensity at 100 11. la Ihe TCS Ggh1.104.

2 1.9

18

1.7

16

1.5

C4

1.3

1.2 Ll I

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

-90 -70 -50 -30 -10 I0 30 50 70 90

mgk.lrm obaervna visw.nagatiwe IeII -- posh hwiumlal

Vertical Intensity at 100 11. la the TCS Sshl.104.

.ngk.lrm obmaverm viewregalive down -- peak vertical

FIGURE C-13. ANGULAR INTENSITY AT 100 FEET, TCS f104

C-13

APPENDIX D

MATHEMTICAL DESCRIPTIONS USED I N THE DEVELOPMENT OF THE CURVED APPROACH SIMULATION

APPENDIX D

MATHEMATICAL DESCRIPTIONS USED I N THE DEVELOPMENT OF THE CURVED APPROACH SIMULATION

Backqround

Figure D-1 represents t h e schematic dep ic t ion o f a locomotive engi- neer (Observer) t r a v e l i n g around a bend toward a parked ( o r slow-moving) t r a i n w i t h a rear-end t r a i n marker. A 90° viewing angle between t h e observer 's l i n e - o f - s i g h t and t h e marker's e m i t t e r l i n e (a 1 i n e perpendicular t o t h e plane o f t h e marker) i s assumed t o be t h e maximum angle worth considering. This i s because, beyond 90°, t h e observer i s e s s e n t i a l l y on t h e o ther s ide o f t h e marked t r a i n ca r and presumably would no t see t h e marker. (Of course, t h e observer might p i c k up secondary cues such as l i g h t r e f l e c t i o n s from t h e ground o r o the r objects) .

The Statement o f Work (SOW) s ta tes t h a t a t l e a s t 1000' o f unobscured 1 i n e o f s i g h t f o r t h e observer (0) i s requ i red f o r t h e t e s t . For convenience, then, t h i s i s used as t h e diameter o f t h e h a l f - c i r c l e i n F igure D-1. From t h i s t h e f o l l o w i n g r e s u l t s a re obtained:

Radius = r = 500'

Circumference (whole c i r c l e ) = C = 2 r r = Zr(500) = 3141.6'

Circumference ( h a l f c i r c l e ) = C 1 = C/2 = 1570.8'

De ree o f t rack: The FRA def ines the degree o f t r a c k curvature as t h e angle ihlr su t e n ed y a 100' chord j o i n i n g two p o i n t s on t h e curve. Thus, given a curve o f , say lZO, one can f i n d t h e radius as fo l l ows (see Figure D-2 f o r c l a r i f i c a t i o n ) :

a) f i n d t a n (812) = (100'/2)/x ==> x = 50 ' / ( tan(e/2))

b) use t h e Pythagorean Theorem t o f i n d t h e radius, r:

The diameter o f a 12' c i r c u l a r t rack , then, i s 2(478.3') o r 956.7'. S i m i l a r l y , given a radius, r, i t i s s t r a i g h t forward t o compute t h e degree o f curvature. The angle, e, subtended by a 100' chord i s given by t h e f o l l o w i n g formula:

e = 2 * a rcs in (501/ r )

Thus, i f one considers t h e rad ius o f 500' used i n t h i s f i e l d t e s t , t h e degree of t r a c k curvature simulated was:

TRAIN MARKER

FIGURE D-1. GEOMETRY OF A CURVED TRACK APPROACH TOWARD A REAR-END TRAIN MARKER

FIGURE D-2. GEOHETRY OF THE DEFINITION OF DEGREE OF TRACK CURVATURE

FIGURE D-3. GEWTRY OF M E FORMULA FOR COMPUTING VIEWING DISTANCES

0-3

C i r c u l a r distance: The c i r c u l a r d is tance (i .e., t r a c k stopping distance) associated w i t h any detec t ion angle, 8, i s given by:

C i r c u l a r d is tance = CD = e *2r = e*(lOOO1)

where 0 5 e 5 r/2 radians,

e i s "viewing angle", i .e, angle between marker 's e m i t t e r l i n e and 0 ' s l i n e o f s igh t .

The Federal Rai 1 road Admini s t r a t i o n (FRA) has ind i ca ted they want markers t o be d e t e c t i b l e such tha t , assuming a "slow approach" (15 mph) , the re i s a t l e a s t 1000' o f t r a c k stopping d is tance ava i l ab le t o t h e locomotive engineer upon detec t ing t h e marker o f another parked o r slow-moving t r a i n . Excluding observer reac t i on time, the momentum o f t h e t r a i n , t h e delays associated w i t h t h e braking system, etc., Given a c i r c u l a r t r a c k o f rad ius 5001, a 1000' r a d i a l stopping d is tance impl ies t h a t marker 's should be d e t e c t i b l e a t a viewing angle, e, o f 57.3" o r more, i.e.,

e = 1 rad ian = 57.3"

Marker r a t e o f tu rn : One i n t e n t o f t h e f i e l d t e s t was t o s imulate a 15 mph (i .e., 22'/sec) approach on 11.5O t rack . To determine t h e r a t e a t which t h e marker should be rotated, f o r a c i r c u l a r t r a c k o f rad ius 5001,

a) Note t h a t t h e circumference o f t h e h a l f c i r c l e i s C ' = 1570.8';

b) a t 22'/sec, i t would take a t r a i n . 1570.8'/22'/sec = 71.4 sec t o d r i v e around t h e h a l f c i r c l e ;

c) assuming up t o 90° o f marker r o t a t i o n i n t h i s study,

Marker r a t e o f t u r n = 90°/71.4 sec = 1.26*/sec

The f i e l d t e s t r a t e o f t u r n was rounded t o 1.25O/sec f o r ease o f c a l i b r a t i o n .

Viewing distance: (See Figure D-3). A t a de tec t ion angle, e, t h e opera tor 's 1 i n e o f s i g h t forms a chord w i t h one end attached a t t he marker, t he o ther end a t t h e observer 's eye. From t h i s , t h e viewing d is tance i s computed as f o l lows:

cos(90° - 8 ) = x / r = = > x = r * cos(90° - 8 ) f o r O ~ e ~ 9 0 °

and Viewing Distance = VD = 2 * (r * cos(90° - 6)) f o r 0 5 8 c - 90"

For example, w i t h a detec t ion angle o f 85O and 11.5" t rack , t h e viewing d is tance ( i n a r e a l wor ld s e t t i n g ) would be:

Recal l t h a t subjects i n the f i e l d t e s t always worked a t a viewing d is tance o f 1000'. The above ca lcu la t i ons i n d i c a t e t h a t , over t h e range o f de tec t ion angles observed i n t h i s t e s t , small d i f fe rences between actual and simulated viewing distances e x i s t . While not e m p i r i c a l l y evaluated, these are d i f fe rences are considered neg l i g ib le . This i s because t h e markers acted e s s e n t i a l l y as p o i n t sources o f l i g h t and detec t ion i s thought t o be essen- t i a l l y a form o f i n t e n s i t y d i sc r im ina t ion o f t he ob jec t from i t s surround (Riggs, 1971, p. 290).

Taken together , t h e above r e s u l t s suggested an a1 t e r n a t i v e method- ology which would make i t eas ier t o se t up t r i a l s and c o l l e c t data from more observers (under d i f f e r e n t condi t ions) . As an observer t r a v e l s around a bend and approaches a t r a i n marker, t h e angle e between t h e marker 's e m i t t e r l i n e and t h e observer 's 1 i n e o f s i g h t grows smal ler and t h i s 'exposes' more o f t h e marker t o t h e observer. The angle e, then, determines t h e marker 's detect ion. The angle can a l so be d i r e c t l y r e l a t e d t o stopping distances as was prev ious ly demonstrated. It was then conceivable t o conduct marker de tec t i on t e s t s w i t h markers mounted on a r o t a t i n g stand o r tu rn tab le . An observer was s i t u a t e d a t a f i x e d d is tance o f 1000' from t h e tu rn tab le . A t r i a l s t a r t e d w i t h an angle o f 90' (o r more) between the e m i t t e r 1 i n e and t h e observer 's 1 i n e o f s i g h t so t h e observer could not see t h e marker. The t u r n t a b l e was then ro ta ted s lowly toward t h e observer u n t i l t h e observer s ignaled t h a t he/she detected the marker. The detec t ion angle was recorded as the dependent v a r i a b l e and then used t o assess the e f f e c t s o f var ious markers (and o the r fac to rs ) on the abi 1 i t y o f human observers t o see them.

APPENDIX E

STATISTICAL TESTS FOR MARKERS

APPENDIX E

STATISTICAL TESTS FOR MARKERS

An Analysis o f Variance (ANOVA) was performed using SAS, a software system f o r data analysis. An ANOVA i s a s t a t i s t i c a l technique t h a t i s used t o study t h e v a r i a b i l i t y o f data. Several values are ca lcu la ted as a r e s u l t o f t he ANOVA. These are:

F = t h e r a t i o o f [Variance explained by f a c t o r s ] / [ ~ a r i a n c e l e f t - unexplained]

P = t h e p r o b a b i l i t y o r l i k e l i h o o d o f saying t h a t a s i g n i f i c a n t - d i f fe rence e x i s t s between markers when the re r e a l l y i s no s i g n i f i c a n t d i f fe rence.

MS = Mean Squared Error , t he v a r i a b i l i t y i n t h e r e s u l t s which 4 i s no t a t t r i b u t e d t o the marker.

ANOVA r e s u l t s f o r a1 1 markers are as fo l lows:

Duncan's Test. This i s a "post-hoc" t e s t o f pa i r -w ise comparison of measurements upon f i n d i n g t h e s ign i f i cance, F. Even though a l l markers were equal l y acceptable according t o t h e 1000 ft ?.topping d is tance c r i t e r i o n , t he re were s t a t i s t i c a l l y r e l i a b l e d i f fe rences among them, F(7,161) = 5282.82, P < 0.0001, MSe = 6.86. Duncan's m u l t i p l e range t e s t i nd i ca ted t h a t , w i t h alpha = .05, t h e mean detec t ion angles were s i g n i f i c a n t l y d i f f e r e n t among markers E, D, H, and A; these are Star yel low/no b l i n k , s t a r red /b l i nk , s t a r red/no b l i n k , and s t a r ye1 low/no b l i n k markers, respect ive ly . Markers C, F, and G (TCS ye1 1 ow/bl i n k , TCS red/b l ink , and DSL markers, respect i vely) were s i g n i f i c a n t l y d i f f e r e n t f o r those j u s t l i s t e d but no t among themselves. F i n a l l y , Marker G ( the Pulse LED) was s i g n i f i c a n t l y d i f f e r e n t from t h e o the r markers.

Means f o r red and ye1 low markers, averaged over both marker. manufacturers, were not s t a t i s t i c a l l y d i f f e r e n t (F(1,23) = .07, P < ,7974, MSe = 9.46). Means f o r S ta r and TCS markers, averagea over red and ye1 1 ow, were s t a t i s t i c a l l y d i f f e r e n t (!(1,23) = 17353.0, P < .0001, MS = 6.56). There was a lso a s i g n i f i c a n t Color x Manufacturer i n t e r a c t i o n ( ~ ( ~ ~ 2 3 ) = 79.79, - P < .OOOl , MS, = 9.17).

The ana lys is o f variance ind ica ted no s i g n i f i c a n t main e f f e c t o f c o l o r (F(1, 23) = 2.32, P < .1411, MS, = 6.41). S i m i l a r l y , t he re was no main e f f e c t f<r c y c l e (r(l, 23r = 0.21, P < .7277, MSe = 11.7). There was, however, a s i g n i f i c a n t i n t e r a c t i o n Letween c o l o r and cyc le (1(1,23) = 89.86, - P < .0001, MS, = 11.2).